The 24th of Dhu Al-Hijjah marks the event of Al-Mubahala (imprecation) of the Holy Prophet (prayers and Allah's peace be upon him and his holy Household), as in this day, the Christians of Najran responded to the call of the Messenger of Allah (prayers and Allah's peace be upon him and his holy Household) for Mubahala, in a memorable moment and blessed day in which the Almighty has shown the status of Ahl Al-Bayt (peace be upon them), the highest position of the eternal sanctity, and the day of Al-Mubahala is one of the great clear proofs of their infallibility and purity status, the day in which the divine light resplended for the Prophet's mission, and a memorable day in which the supreme word of God shined and gave victory to Islam.
The verse 61 of Chapter Aal Imran is called the verse of al-Mubahala: {O Messenger! If they dispute with you in this matter after the knowledge has come to you, then, say, 'Come, let us call our sons and your sons, and our women and your women, and our souls and your souls. Then let us earnestly invoke and lay the malison (curse) of Allah on those who lie.} (3:60-61) Al-Mubahalah' (Arabic: المباهلة) is derived from the Arabic word 'Bahlah' (curse), so the term 'Mubahala' means cursing each other. In Islamic tradition it refers to the ancient ceremony of mutually and formally calling God's curse down upon whichever of the two parties was not speaking truthfully. This verse was revealed in the argument that took place between the Messenger of Allah (prayer and Allah's peace be upon him and his holy Household) and the Christians of Najran.
The Holy Prophet (prayers and Allah's peace be upon him and his holy Household) wrote a letter to Abi Harithah, the Bishop of Najran in which he called the people of Najran to Islam, Abu Harithah then consulted a group of his people, and he was their monk, master and teacher and the Romans kings had built churches for him and gave him a honorable status for his knowledge and diligence in religion. So they decided to send a representative deputation od sixty men from the nobles ans scholars of Najran to meet and negotiate with the Messenger of Allah (prayers and Allah's peace be upon him and his holy Household), and once they arrived to Medina, the long discussion and argumentation between the two parties was to no avail, the Holy Prophet (prayers and Allah's peace be upon him and his holy Household) invited them to embrace Islam but the Christians of Najran remained obstinate and refused to be convinced by anything. Thereupon the following verse 61 from Chapter 3 Aal 'Imran was revealed: {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 ourselves and yourselves, then let us be earnest in prayer, and invoke the curse of Allah on the liars.} (3:61) Now the Holy Prophet reproduced the Quranic verse before the deputation of the Christians and declared the challenge of 'Mubahala'. They accepted it and fixed a date for it, and it was the 24th of Dhu Al-Hijjah 10 AH, and the Almighty God has chosen for the Messenger of Allah (prayers and Allah's peace be upon him and his holy Household) the people that will do the "Mubahala" with him as stated in the verse, and they are: "Al-Hassan and Al-Hussayn" as "our sons", "Fatima" as "our women" and "Ali Ibn Abi Taleb" as "ourselves" (prayers and Allah's peace be upon them all).
But on the promised day, when the Christians of Najran saw that the Holy Prophet (prayers and Allah's peace be upon him and his holy Household) was accompanied by the dearest people to him; Ali Ibn Abi Taleb, his daughter Fatima and Al-Hassan and Al-Hussayn (prayers and Allah's peace be upon them all) and has knelt in preparation of Al-Mubahala. But on seeing the radiant faces of these sinless members of the household of the Prophet, the Christians got scared. They decided not to seek Mubahala anymore but accepted their defeat. They agreed to pay tribute and returned home.
'Allamah Al-Turayhi the author of the book "Majma' Al-Bahrayn" said: "And they asked for a moment to consult, and once they met their wiser master, Abd Al-Maseeh, he told them: I swear by God that you recognized that Mohammad is a Messenger and brought you the proof for that. I swear by God that no people that have been imprecated by a prophet neither could live nor their children could grow, so if you refuse to leave your religion, bid the man farewell and go away to your country. And that after that the Holy Prophet took the hand of Ali and in hands Al-Hassan and Al-Hussayn and behind him Fatima (peace be upon them all), the opposing group of the Christians of Najran were awestruck and spellbound. Abu Harithah, the greatest scholar among them, addressed his people: "Verily I see a divine light on the face of our combatants; I am beholding such faces among them as can make the mountains move from their spots if they pray to God. So beware! Never try to contest with them, otherwise you will perish and the entire nation of Christians will succumb to extinction!" So they said: O Aba Al-Qassem, we will not imprecate [do the Mubahala] you but we make peace with you, and so did the Messenger of Allah (prayers and Allah's peace be upon him and his holy Household) a peace treaty was signed on the terms that the Christians of Najran would thereby be committed to pay the Holy Prophet an annual tribute consisting of two thousand costumes-worth; one thousand in the month of Safar and the other thousand int he month of Rajab, and a loan of thirty armors and a loan of thirty horses and thirty spears.
The Holy Prophet (prayers and Allah's peace be upon him and his holy Household) said: "I swear by God, who my soul is in His grasp, that death of the people of Najran had become close and if they engaged in mubahala with me, they surely would turn into monkeys and pigs and their whole land would burn and they would burn and God would destroy all the people of Najran and even birds would not remain on their trees and all Christians would die in less than a year."
And also on this day the Commander of the Faithful Ali Ibn abi Taleb (peace be upon both of them) gave his ring as alms while bowing in the prayer in the Masjid of the Holy Prophet (prayers and Allah's peace be upon him and his holy Household) and this verse was revealed: {Only God, His Messenger, and the true believers who are steadfast in prayer and pay alms, while they kneel during prayer, are your guardians} (5:55)