Diplomatic career of Muhammad

Location of the Kingdom of Aksum.

Muhammad's commencement of public preaching brought him stiff opposition from the leading tribe of Mecca, the Quraysh. Although Muhammad himself was safe from persecution due to protection from his uncle, Abu Talib (a leader of the Banu Hashim, one of the main clans that formed the Quraysh), some of his followers were not in such a position. A number of Muslims were mistreated by the Quraysh, some reportedly beaten, imprisoned, or starved.[9] In 615, Muhammad resolved to send fifteen Muslims to emigrate to Axum to receive protection under the Christian ruler, the Negus, Aṣḥama ibn Abjar.[10] Emigration was a means through which some of the Muslims could escape the difficulties and persecution faced at the hands of the Quraysh,[2] it also opened up new trading prospects.[11]

The Quraysh, on hearing the attempted emigration, dispatched a group led by 'Amr ibn al-'As and Abdullah ibn Abi Rabi'a ibn Mughira in order to pursue the fleeing Muslims. The Muslims reached Axum before they could capture them, and were able to seek the safety of the Negus in Harar. The Qurayshis appealed to the Negus to return the Muslims and they were summoned to an audience with the Negus and his bishops as a representative of Muhammad and the Muslims, Ja`far ibn Abī Tālib acted as the ambassador of the Muslims and spoke of Muhammad's achievements and quoted Qur'anic verses related to Islam and Christianity, including some from Surah Maryam.[12] Ja`far ibn Abī Tālib is quoted according to Islamic tradition as follows:

O king! We were plunged in the depth of ignorance and barbarism; we adored idols, we lived in unchastity, we ate the dead bodies, and we spoke abominations, we disregarded every feeling of humanity, and the duties of hospitality and neighbourhood were neglected; we knew no law but that of the strong, when Allah raised among us a man, of whose birth, truthfulness, honesty, and purity we were aware; and he called to the Oneness of Allah and taught us not to associate anything with Him. He forbade us the worship of idols; and he enjoined us to speak the truth, to be faithful to our trusts, to be merciful and to regard the rights of the neighbours and kith and kin; he forbade us to speak evil of women, or to eat the substance of orphans; he ordered us to fly from the vices, and to abstain from evil; to offer prayers, to render alms, and to observe fast. We have believed in him, we have accepted his teachings and his injunctions to worship Allah and not to associate anything with Him, and we have allowed what He has allowed, and prohibited what He has prohibited. For this reason, our people have risen against us, have persecuted us in order to make us forsake the worship of Allah and return to the worship of idols and other abominations. They have tortured and injured us, until finding no safety among them, we have come to your country, and hope you will protect us from oppression.[13][14]

The Negus, seemingly impressed, consequently allowed the migrants to stay, sending back the emissaries of Quraysh.[12] It is also thought that the Negus may have converted to Islam.[15] The Christian subjects of the Negus were displeased with his actions, accusing him of leaving Christianity, although the Negus managed to appease them in a way which, according to Ibn Ishaq, could be described as favourable towards Islam.[12] Having established friendly relations with the Negus, it became possible for Muhammad to send another group of migrants, such that the number of Muslims living in Abyssinia totalled around one hundred.[10]

Road to Ta'if in the foreground, mountains of Ta'if in the background (Saudi Arabia).

In early June 619, Muhammad set out from Mecca to travel to Ta'if in order to convene with its chieftains, and mainly those of Banu Thaqif (such as 'Abd-Ya-Layl ibn 'Amr).[16] The main dialogue during this visit is thought to have been the invitation by Muhammad for them to accept Islam, while contemporary historian Montgomery Watt observes the plausibility of an additional discussion about wresting the Meccan trade routes that passed through Ta'if from Meccan control.[6] The reason for Muhammad directing his efforts towards Ta'if may have been due to the lack of positive response from the people of Mecca to his message until then.[2]

In rejection of his message, and fearing that there would be reprisals from Mecca for having hosted Muhammad, the groups involved in meeting with Muhammad began to incite townsfolk to pelt him with stones.[6] Having been beset and pursued out of Ta'if, the wounded Muhammad sought refuge in a nearby orchard.[17] Resting under a grape vine, it is here that he invoked God, seeking comfort and protection.[18][19]

According to Islamic tradition, Muhammad on his way back to Mecca was met by the angel Gabriel and the angels of the mountains surrounding Ta'if, and was told by them that if he willed, Ta'if would be crushed between the mountains in revenge for his mistreatment. Muhammad is said to have rejected the proposition, saying that he would pray in the hopes of succeeding generations of Ta'if coming to accept Islamic monotheism.[18][20]

Hajj pilgrims at Mina

In the summer of 620 during the pilgrimage season, six men of the Khazraj travelling from Medina came into contact with Muhammad. Having been impressed by his message and character, and thinking that he could help bring resolution to the problems being faced in Medina, five of the six men returned to Mecca the following year bringing seven others. Following their conversion to Islam and attested belief in Muhammad as the messenger of God, the twelve men pledged to obey him and to stay away from a number of Islamically sinful acts. This is known as the First Pledge of al-'Aqaba by Islamic historians.[21] Following the pledge, Muhammad decided to dispatch a Muslim ambassador to Medina and he chose Mus'ab ibn 'Umair for the position, in order to teach people about Islam and invite them to the religion.[22]

With the slow but steady conversion of persons from both the Aws and Khazraj present in Medina, 75 Medinan Muslims came as pilgrims to Mecca and secretly convened with Muhammad in June 621, meeting him at night. The group made to Muhammad the Second Pledge of al-'Aqaba, also known as the Pledge of War.[21] The people of Medina agreed to the conditions of the first pledge, with new conditions including included obedience to Muhammad, the enjoinment of good and forbidding evil. They also agreed to help Muhammad in war and asked of him to declare war on the Meccans, but he refused.[23]

Some western academics are noted to have questioned whether or not a second pledge had taken place, although William M. Watt argues that there must have been several meetings between the pilgrims and Muhammad on which the basis of his move to Medina could be agreed upon.[24]

The demography of Medina before Muslim migration consisted mainly of two pagan Arab tribes; the Aws and the Khazraj; and at least three Jewish tribes: the Qaynuqa, Nadir, and Qurayza.[2] Medinan society, for perhaps decades, had been scarred by feuds between the two main Arab tribes and their sub-clans. The Jewish tribes had at times formed their own alliances with either one of the Arab tribes. The oppressive policy of the Khazraj who at the time had assumed control over Medina, forced the Jewish tribes, Nadir and Qurayza, into an alliance with the Aws, who had been significantly weakened. The culmination of this was the Battle of Bu'ath in 617, in which the Khazraj and their allies, the Qaynuqa, had been soundly defeated by the coalition of Aws and its supporters.[1][25]

Although formal combat between the two clans had ended, hostilities between them continued even up until Muhammad's arrival in Medina. Muhammad had been invited by some Medinans, who had been impressed by his religious preaching and manifest trustworthiness, as an arbitrator to help reduce the prevailing factional discord.[26] Muhammad's task would thus be to form a united community out of these heterogeneous elements, not only as a religious preacher, but as a political and diplomatic leader who could help resolve the ongoing disputes.[2] The culmination of this was the Constitution of Medina.

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Constitution of Medina

After the pledges at al-'Aqaba, Muhammad received promises of protection from the people of Medina and he migrated to Medina with a group of his followers in 622, having escaped the forces of Quraysh. They were given shelter by members of the indigenous community known as the Ansar. After having established the first mosque in Medina (the Masjid an-Nabawi) and obtaining residence with Abu Ayyub al-Ansari,[27] he set about the establishment of a pact known as the Constitution of Medina (Arabic: صحيفة المدينة, romanized: Sahifat ul-Madinah, lit. 'Charter of Medina'). This document was a unilateral declaration by Muhammad, and deals almost exclusively with the civil and political relations of the citizens among themselves and with the outside.[28]

The Constitution, among other terms, declared:

• the formation of a nation of Muslims (Ummah) consisting of the Muhajirun from the Quraysh, the Ansar of Yathrib (Medina) and other Muslims of Yathrib.
• the establishment of a system of prisoner exchange in which the rich were no longer treated differently from the poor (as was the custom in pre-Islamic Arabia)
• all the signatories would unite as one in the defense of the city of Medina, declared the Jews of Aws equal to the Muslims, as long as they were loyal to the charter.
• the protection of Jews from religious persecution
• that the declaration of war can only be made by Muhammad.

The source of authority was transferred from public opinion to God.[28] Bernard Lewis writes the community at Medina became a new kind of tribe with Muhammad as its sheikh, while at the same time having a religious character.[29] Watt argues that Muhammad's authority had not extended over the entirety of Medina at this time, such that in reality he was only the religious leader of Medina, and his political influence would only become significant after the Battle of Badr in 624.[30] Lewis opines that Muhammad's assumption of the role of statesman was a means through which the objectives of prophethood could be achieved.[31] The constitution, although recently signed, was soon to be rendered obsolete due to the rapidly changing conditions in Medina,[2] and with the exile of two of the Jewish tribes and the execution of the third after having been accused of breaching the terms of agreement.

The signing of the constitution could be seen as indicating the formation of a united community, in many ways, similar to a federation of nomadic clans and tribes, as the signatories were bound together by solemn agreement. The community, however, now also had a religious foundation.[32] Extending this analogy, Watt argues that the functioning of the community resembled that of a tribe, such that it would not be incorrect to call the community a kind of "super-tribe".[32] The signing of the constitution itself displayed a degree of diplomacy on part of Muhammad, as although he envisioned a society eventually based upon a religious outlook, practical consideration was needed to be inclusive instead of exclusive of the varying social elements.[2]

Both the Aws and Khazraj had progressively converted to Islam, although the latter had been more enthusiastic than the former; at the second pledge of al-'Aqaba, 62 Khazrajis were present, in contrast to the 3 members of the Aws; and at the Battle of Badr, 175 members of the Khazraj were present, while the Aws numbered only 63.[33] Subsequently, the hostility between the Aws and Khazraj gradually diminished and became unheard of after Muhammad's death.[1] According to Muslim scholar al-Mubarakpuri, the 'spirit of brotherhood' as insisted by Muhammad amongst Muslims was the means through which a new society would be shaped.[34]

The result was Muhammad's increasing influence in Medina, although he was most probably only considered a political force after the Battle of Badr, more so after the Battle of Uhud where he was clearly in political ascendency.[35] To attain complete control over Medina, Muhammad would have to exercise considerable political and military skills, alongside religious skills over the coming years.[26]

In March 628, Muhammad saw himself in a dream performing the Umrah (lesser pilgrimage),[36] and so prepared to travel with his followers to Mecca in the hopes of fulfilling this vision. He set out with a group of around 1,400 pilgrims (in the traditional ihram garb[37]). On hearing of the Muslims travelling to Mecca for pilgrimage, the Quraysh sent out a force of 200 fighters in order to halt the approaching party. In no position to fight, Muhammad evaded the cavalry by taking a more difficult route through the hills north of Mecca, thereby reaching al-Hudaybiyya, just west of Mecca.[38]

It was at Hudaybiyyah that a number of envoys went to and fro in order to negotiate with the Quraysh. During the negotiations, Uthman ibn Affan was chosen as an envoy to convene with the leaders in Mecca, on account of his high regard amongst the Quraysh.[39] On his entry into Mecca, rumours ignited among the Muslims that 'Uthman had subsequently been murdered by the Quraysh. Muhammad responded by calling upon the pilgrims to make a pledge not to flee (or to stick with Muhammad, whatever decision he made) if the situation descended into war with Mecca. This pledge became known as the Pledge of Good Pleasure (Arabic: بيعة الرضوان, romanized: Bay'at ar-Ridhwān) or the Pledge Under The Tree.[38]

The incident was mentioned in the Qur'an in Surah 48:[38]

Allah's Good Pleasure was on the Believers when they swore Fealty to thee under the Tree: He knew what was in their hearts, and He sent down Tranquillity to them; and He rewarded them with a speedy Victory;

— Translated by Yusuf Ali, Sura 48 (Al-Fath), ayah 18[40]

Soon afterwards, with the rumour of Uthman's slaying proven untrue, negotiations continued and a treaty was eventually signed between the Muslims and Quraysh. Conditions of the treaty included:[41]

• the Muslims' postponement of the lesser pilgrimage until the following year
• a pact of mutual non-aggression between the parties
• a promise by Muhammad to return any member of Quraysh (presumably a minor or woman) fleeing from Mecca without the permission of their parent or guardian, even if they be Muslim.

Some of Muhammad's followers were upset by this agreement, as they had insisted that they should complete the pilgrimage they had set out for. Following the signing of the treaty, Muhammad and the pilgrims sacrificed the animals they had brought for it, and proceeded to return to Medina.[38] It was only later that Muhammad's followers would realise the benefit behind this treaty.[2] These benefits, according to Islamic historian Welch Buhl, included the inducing of the Meccans to recognise Muhammad as an equal; a cessation of military activity, boding well for the future; and gaining the admiration of Meccans who were impressed by the incorporation of the pilgrimage rituals.[2]

The treaty was set to expire after 10 years, but was broken after only 10 months.[38] According to the terms of the treaty of Hudaybiyyah, the Arab tribes were given the option to join either of the parties, the Muslims or Quraish. Should any of these tribes face aggression, the party to which it was allied would have the right to retaliate. As a consequence, Banu Bakr joined Quraish, and the Banu Khuza‘ah joined Muhammed.[42] Banu Bakr attacked Banu Khuza'ah at al-Wateer in Sha'baan 8 AH and it was revealed that the Quraish helped Banu Bakr with men and arms taking advantage of the cover of the night.[42] Pressed by their enemies, the tribesmen of Khuza‘ah sought the Holy Sanctuary, but here too, their lives were not spared, and Nawfal, the chief of Banu Bakr, chasing them in the sanctified area, massacred his adversaries.

Purported letter sent by Muhammad to Emperor Heraclius; reproduction taken from Majid Ali Khan, Muhammad The Final Messenger Islamic Book Service, New Delhi (1998).

A letter was sent from Muhammad to the emperor of the Byzantine Empire, Heraclius, through the Muslim envoy Dihyah bin Khalifah al-Kalbi, although Shahid suggests that Heraclius may never have received it.[4] He also advances that more positive sub-narratives surrounding the letter contain little credence. According to Nadia El Cheikh, Arab historians and chroniclers generally did not doubt the authenticity of Heraclius' letter due to the documentation of such letters in the majority of both early and later sources.[46] Furthermore, she notes that the formulation and the wordings of different sources are very close and the differences are ones of detail: They concern the date on which the letter was sent and its exact phrasing.[46] Muhammad Hamidullah, an Islamic research scholar, argues for the authenticity of the letter sent to Heraclius, and in a later work reproduces what is claimed to be the original letter.[46][47]

The account as transmitted by Muslim historians is translated as follows:[46]

In the name of God, the Gracious One, the Merciful
From Muhammad, servant of God and His apostle to Heraclius, premier of the Romans:
Peace unto whoever follows the guided path!
Thereafter, verily I call you to submit your will to God. Submit your will to God and you will be safe. God shall compensate your reward two-folds. But if you turn away, then upon you will sins of the peasants.
Then "O People of the Scripture, come to a term equitable between us and you that we worship none but God and associate with Him nothing, and we take not one another as Lords apart from God. But if they turn away, then say: Bear witness that we peace makers."^{[Quran 3:64]}
Seal: Muhammad, Apostle of God

According to Islamic reports, Muhammad dispatched Dihyah al-Kalbi[48][49] to carry the epistle to "Caesar" through the government of Bosra after the Byzantine defeat of the Persians and reconquest of Jerusalem.[50][51][48] Islamic sources say that after the letter was read to him, he was so impressed by it that he gifted the messenger of the epistle with robes and coinage.[52] Alternatively, he also put it on his lap.[50] He then summoned Abu Sufyan ibn Harb to his court, at the time an adversary to Muhammad but a signatory to the then-recent Treaty of Hudaybiyyah, who was trading in Greater Syria at the time. Asked by Heraclius about the man claiming to be a prophet, Abu Sufyan responded, speaking favorably of Muhammad's character and lineage and outlining some directives of Islam. Heraclius was seemingly impressed by what he was told of Muhammad, and felt that Muhammad's claim to prophethood was valid.[46][53][54] Later reportedly he wrote to a certain religious official in Rome to confirm if Muhammad's claim of prophethood was legitimate, and, after receiving the reply to his letter, called the Roman assembly saying, "If you desire salvation and the orthodox way so that your empire remain firmly established, then follow this prophet," to the rejection of the council.[52][55][50] Heraclius eventually decided against conversion but the envoy was returned to Medina with the felicitations of the emperor.[42]

Scholarly historians disagree with this account, arguing that any such messengers would have received neither an imperial audience or recognition, and that there is no evidence outside of Islamic sources suggesting that Heraclius had any knowledge of Islam.[56]

The letter inviting Armah, the Axumite king of Ethiopia/Abyssinia, to Islam had been sent by Amr bin 'Umayyah ad-Damri, although it is not known if the letter had been sent with Ja'far on the migration to Abyssinia or at a later date following the Treaty of Hudaybiyyah. According to Hamidullah, the former may be more likely.[5] The letter is translated as:

In the name of God, the Gracious One, the Merciful
From Muhammad, Apostle of God to the Negus, premier of the Abyssinians:
Peace unto whoever follows the guided path!
Thereafter, verily to you I make praise of God, but Whom there is no god, the King, the Holy One, the [Maker of] Peace, the Giver of Faith, the Giver of Security. And I bear witness that Jesus son of Mary is the Spirit of God and His Word that He cast into the Virgin Mary, the immaculate [and] the immune, and she was impregnated with Jesus by His Spirit and His blow like how He created Adam with His Hand. And I verily call you to the one God with no partner [associated in worship] to Him, and adherence upon His obedience, and that you follow me and believe in that which came to me, [for] I, in fact, am the Apostle of God and verily call you and your hosts toward God, [Possessor of] Might and Majesty.
And thus I have informed and sincerely admonished. So accept my sincere admonition. "And Peace unto whoever follows the guided path."^{[Quran 20:47]}
Seal: Muhammad, Apostle of God

Having received the letter, the Negus was purported by some muslim sources to accept Islam in a reply he wrote to Muhammad. According to Islamic tradition, the Muslims in Medina prayed the funeral prayer in absentia for the Negus on his death.However there are no evidence for these claims with even some Muslim historians question them.[57] It is possible that a further letter was sent to the successor of the late Negus.[5]

Drawing of the letter of the Prophet Muhammed to Muqauqis, which was discovered in Egypt in 1858.[58]

There has been conflict amongst scholars about the authenticity of aspects concerning the letter sent by Muhammad to Muqawqis. Some scholars such as Nöldeke consider the currently preserved copy to be a forgery, and Öhrnberg considers the whole narrative concerning the Muqawqis to be "devoid of any historical value".[59] Muslim historians, in contrast, generally affirm the historicity of the reports. The text of the letter (sent by Hatib bin Abu Balta'ah) according to Islamic tradition is translated as follows:

In the name of God, the Gracious One, the Merciful
From Muhammad, servant of God and His apostle to al-Muqawqis, premier of Egypt:
Peace unto whoever follows the guided path!
And thereafter, verily I call you to the call of Submission [to God] ("Islam"). Submit (i.e., embrace Islam) and be safe [from perdition, as] God shall compensate your reward two-folds. But if you turn away, then upon you will be the guilt [of delusion] of the Egyptians.
Then "O People of the Scripture, come to a term equitable between us and you that we worship none but God and associate [as partners in worship] with Him nothing, and we take not one another as Lords apart from God. [Then God says] But if they turn away, then say: Bear witness that we are Submitters [to God] ("Muslims")."^{[Quran 3:64]}
Seal: Muhammad, Apostle of God[60]

The Muqawqis responded by sending gifts to Muhammad, including two female slaves, Maria al-Qibtiyya and Sirin. Maria became the concubine of Muhammad,[61] with some sources reporting that she was later freed and married. The Muqawqis is reported in Islamic tradition as having presided over the contents of the parchment and storing it in an ivory casket, although he did not convert to Islam.[62]

The letter to Khosrow II (Arabic: كِسْرٰى, romanized: Kisrá) is translated by Muslim historians as:

In the name of God, the Gracious One, the Merciful
From Muhammad, Apostle of God to Khosrow, premier of Persia:
Peace unto whoever follows the guided path, and believes in God and His apostle, and bears witness that there is no god but the one God with no partner [associated in worship] to Him and that Muhammad is His servant and His apostle!
And [hence] I call you to the call of God, [for] in fact I am the apostle of God to mankind in its entirety, "that he may warn whoever is [spiritually] alive and [God's] word is proven against the infidels (i.e., those without faith in God)."^{[Quran 36:70]}
So submit [to God] (i.e., embrace Islam) and be safe [from perdition]. But if you refuse, then verily will the guilt [of delusion] of the Zoroastrians ("Magians") be upon you.
Seal: Muhammad, Apostle of God

According to Muslim tradition, the letter was sent through Abdullah as-Sahmi[lower-alpha 1][49] who, through the governor of Bahrain, delivered it to the Khosrau.[63] Upon reading it Khosrow II reportedly tore up the document,[64] saying, "A pitiful slave among my subjects dares to write his name before mine"[52] and commanded Badhan, his vassal ruler of Yemen, to dispatch two valiant men to identify, seize and bring this man from Hejaz (Muhammad) to him. When Abdullah ibn Hudhafah as-Sahmi told Muhammad how Khosrow had torn his letter to pieces, Muhammad is said to have stated, "May God [likewise] tear apart his kingdom," while reacting to the Caesar's behavior saying, "May God preserve his kingdom."[65][49]

Letter of the Prophet Muhammed to Munzir b. Sawa (reproduction of a manuscript copy of the letter taken from Sultan Ahmed Qureshi, Letters of the Holy Prophet, Karachi (1983).

Apart from the aforementioned personalities, there are other reported instances of correspondence. Munzir ibn Sawa al-Tamimi, the governor of Bahrain, was apparently an addressee, with a letter having been delivered to him through al-'Alaa al-Hadrami. Some subjects of the governor reportedly converted to Islam, whereas others did not.[66] A similar letter was sent to Hauda bin Ali, the governor of Yamamah, who replied that he would only convert if he were given a position of authority within Muhammad's government, a proposition which Muhammad was unwilling to accept.[66]

Letter of Muhammad to al-Ḥārith bin ʾAbī Shamir al-Ghassānī, who ruled Byzantine Syria (called by Arabs ash-Shām "north country, the Levant" in contrast to al-Yaman "south country, the Yemen") based in Bosra,[lower-alpha 2][67][49] alternatively Damascus,[52][68] and hailed from the Ghassanian dynasty of Hellenized Arabs (comparable though superior in status to the Herodian dynasty of Roman Palestine):

In the name of God, the Gracious One, the Merciful
From Muhammad, Apostle of God to al-Ḥāriṯ the son of ʾAbū Šamir:
Peace unto whoever follows the guided path and believe in God and is sincere [about it]!
Thereby I call you to [this] that you believe in the one God with no partner [associated in worship] to Him [and] your kingship remains yours.
Seal: Muhammad, Apostle of God

Al-Ghassani reportedly reacted less than favourably to Muhammad's correspondence, viewing it as an insult.[66]

Jayfar and 'Abd, princes of the powerful ruling 'Azd tribe which ruled Oman in collaboration with Persian governance, were sons of the client king Juland (frequently spelt Al Julandā based on the Perso-Arabic pronunciation).[69] They embraced Islam peacefully on 630 AD upon receiving the letter sent from Muhammad through 'Amr ibn al-'As.[70] The 'Azd subsequently played a major role in the ensuant Islamic conquests. They were one of the five tribal contingents that settled in the newly founded garrison city of Basra at the head of the Persian Gulf; under their general al-Muhallab ibn Abu Sufrah and also took part in the conquest of Khurasan and Transoxania.[71]

The letter reads as follows:

In the name of God, the Gracious One, the Merciful
From Muhammad, Apostle of God to Jayfar and ʿAbd [sic],[72] the sons of al-Julandī:
Then peace unto whoever follows the guided path!
Thereafter, verily I call you two to the call of Submission [to God] ("Islam"). Submit (i.e., embrace Islam) and be safe I, in fact, am the apostle of God to mankind in its entirety, "that he may warn whoever is alive Then indeed you two: if you consent unto Submission to Allah, I shall patronize you. But if you refuse, then [know that] indeed your reign is fleeting, and my horsemen shall invade into your courtyard, and my prophethood shall become dominate your kingdom.
Seal: Muhammad, Apostle of God

• Al-Ismail, Tahia (1998). The Life of Muhammad: his life based on the earliest sources. Ta-Ha publishers Ltd, United Kingdom. ISBN 0-907461-64-6.
• Hamidullah, Muhammad (1985). Six originaux des lettres du Prophète de l'islam: étude paléographique et historique des lettres. Paris: Tougui. ISBN 2-7363-0005-X.
• Watt, M Montgomery (1981). Muhammad at Medina. United Kingdom: Oxford University Press. ISBN 0-19-577307-1.