"Sixty Christian priests of Najran, headed by Abu Harith bin Aqamah, the grand bishop of Najran, Abdu Massih and Ayham arrived in Medina on 9/631 to clarify their religious and political stance, which had spread over the Arab peninsula and to engage in discussions with the Prophet to realize the essence and truth of Islam.
After lengthy discussions which have been presented in details in Ibn Hisham's Sirah (1:573), no agreement was reached on the position and standing of Jesus. The Christians of Najran believed in the divinity of Jesus and considered him as the son of God. This is while, based on the explicit wording of the Koran (3:59), the Prophet considered him as a prophet and the servant of God. At the end of the discussions, the Prophet suggested that the two sides engage in mubahila (imprecation), in other words, to invoke divine malediction for the lying side. It was an old custom much used by the ancient prophets. Each of the disputant parties was required to swear a solemn oath that they were on the side of the truth, calling on God to wreak His vengeance on them if they lied. In short, mubahila was a custom to invoke the curse of God on the liar. The following verse was revealed in this regard:
"But whoever disputes with you in this matter after what has come to you of knowledge, then say: come let us call our sons and your sons and our women and your women and our near people and your near people, then let us be earnest in prayer, and pray for the curse of God on the liars." (3:61)
The Prophet ordered that in a field outside Medina a thin black aba (men's loose sleeveless cloak open in front) be used as a shade between two trees. The Christian chiefs and dignitaries of Najran stood in orderly ranks on one side of the field, on the other side, the Prophet, together with Ali, Fatima, Hasan and Hussain came from the direction of Medina to the shade. Along this path, the Prophet, holding the hand of Ali, Hasan and Hussain walked in front with Fatima behind them. With such simplicity and grandeur, they reached the shade and stood below the aba. The Prophet recited the tathir verse and addressed the Ahl al-Bayt by saying: "I will invoke malediction for them and you say amin.' When the Christians saw their radiant faces, they were dismayed and overwhelmed. Seeing such glory and grandeur, the Najran chiefs lost their self-confidence and felt that they were very puny and could not stand against the Prophet and his Household. They, therefore, accepted to pay jaziya and agreed to come to the terms. On behalf of the Prophet, Ali bin Abu Talib signed a peace treaty with the Christians.
The Christians were to annually offer twelve thousand exquisite clothes, a thousand mithqal of gold, and some other items to remain Christians under the umbrella of Islam. On the basis of the mubahila verse, Zamakhshari, Baidawi, Fakhruddin Razi and others regard Ali, Fatima, Hasan and Hussain superior to all other people and argue that Hasan and Hussain are the sons of the Prophet.
The term anfusina in the mubahila verse proves the unity of the heart and soul of the Prophet and Ali. The Prophet said, "Ali is of me and I am of Ali." (Fadail al-Khamsah, 1:343). The mubahila tradition has been recounted in different books of Sirah and history with various wordings. These include those of Tirmizi (2:166) which quotes S`ad ibn Abi Waqqas as follows: "When the mubahalah verse was recited, the Prophet summoned Ali, Fatima, Hasan, and Hussain and said: `O God, these are the Members of my Household." This tradition is also narrated by Hakim Nishaburi in al-Mustadrak (3:150) and Bayhaqi in Sunan (7: 63).