The following year, the Christians of Najran came to Madinah to see and to verify the Truth of the Prophet of the Muslims. They remained adamantly opposed to all arguments, or to accept evidence from the scriptures. In the end, they opted to go out in the open for Mubahela (a method employed in the olden times to invoke the curse of Truth over Falsehood).
Allah revealed in al-Quran: "The similitude of Jesus before Allah is as that of Adam; He created him from dust, then said to him Be, and he was. The Truth (comes) from Allah alone; so be not of those who doubt. If anyone disputes in this matter with thee, now after (full) knowledge hath come to thee, say: come! Let us gather together our sons, and your sons, our women and your women, ourselves and yourselves: then let us earnestly pray and invoke the curse of Allah on those who lie!" III: 59-61. Ali accompanied the Prophet with Fatima and their two sons, Hasan and Husain (the five infallible members of the Ahle Bait of the Prophet) at the Mubahela representing the men, the women and the children of all Muslims to face the Christian challengers fi7om Najran for the test of the Truth. Seeing the Prophet and his Ahle Bait, their faces glowing with the light of the Truth, the Christians withdrew from Mubahela and returned home, not converted as Muslims, but in peace with the Muslims and the Islamic State.
In the same year, Sura Tauba was revealed to the Prophet. He sent Abu Bakr to Makkah to deliver it to the pilgrims. But soon, the Archangel Gabriel reappeared with instructions that the Message must be delivered by the Prophet himself or one of his family. The Prophet hastened to dispatched Ali on his personal camel. Ali caught up with Abu Bakr, took charge of the important Divine Proclamation and arrived in Makkah. He proclaimed in the name of Allah the early verses of the Sura Tauba, stating that the city of Makkah would, from then on, be a sanctuary for all Muslims, and forbidding all idolaters and polytheists to enter the Holy Precinct, and forbidding the carrying of idols in the Sanctuary.
In the tenth year of al-Hijra, the Prophet of Islam arrived in Makkah for Hajj with thousands of his followers. Ali was in
at that time. He also arrived in Makkah in time to participate in the Haj, personally conducted by the Prophet. This was one of the most important events in the history of early Islam, and every Muslim wanted to perform Haj with the Prophet. After completion of the Haj, and on the way back to Madinah, the Prophet of Islam was ordained by Allah to carry out the last duty of his Prophetic Mission thus: "O Apostle! Proclaim the (Message) which hath been sent to theefrom thy Lord. If thou didst not, thou wouldst have not fulfilled and proclaimed His Mission. And Allah will defend thee from men (who mean mischief. For Allah guideth not those who reject Faith." V: 70 Yemen
He made a stop at the well called Ghadire Khumm and gathered all those who could be recalled. A makeshift pulpit was erected and the Prophet addressed the congregation: "It seems as if I would soon be summoned to go to Allah and I have responded to it I entrust you with two very precious and grand things,.one of which is greater than the other: the Book of Allah and my Ahle Bait. Take heed of the way you treat these two trusts, because the Qur'an and the Ahle Bait will never separate until they return to me by the Hawd al-Kawthar (the pond). " He then said: "Allah is my master and I am the master of every believer. " Then he took the hand of Ali and raising his arm high above his shoulders for all to see, and said: " Ali will be the maula (master) of whoever deems me his (maula) master. 0 Allah! Place within Your own vilayah whoever accepts the vilayah of Ali and be the enemy of whoever shows animosity to him. " All those who attended the congregation under the hot mid-afternoon sun congratulated Ali on the honor that had just been bestowed upon him by the Will of Allah. This event has been recorded in both Shiite and Sunni books.
It was at this place and occasion when the last revelation of the Qur’an was delivered to the Prophet: "... This day have those who rejected Faith given up hope of your religion: yet fear them not but fear me. This day have I perfected your religion for you, completed My favor upon you, and have chosen for you Islam as your religion. " V:4. This completed the Book of Allah as well as the long and onerous task of the Prophet.
Soon after his return to Madinah the Prophet became ill and passed away. However, while the members of the Ahle Bait were busy making arrangements for the burial of the Prophet, the senior companions hurried to a heated conference that was being held at Saqueefa Banu Saada to determine the successor to the Prophet. At the conclusion of the meeting, Abu Bakr was elected as the first Caliph.