يَا أَيُّهَا الرَّسُولُ بَلِّغْ مَا أُنْزِلَ إِلَيْكَ مِنْ رَبِّكَ ۖ وَإِنْ لَمْ تَفْعَلْ فَمَا بَلَّغْتَ رِسَالَتَهُ ۚ وَاللَّهُ يَعْصِمُكَ مِنَ النَّاسِ ۗ إِنَّ اللَّهَ لَا يَهْدِي الْقَوْمَ الْكَافِرِينَ
O Messenger! Deliver what has been revealed to you from your Lord; and if you do it not, then you have not delivered His message, and Allah will protect you from the people; surely Allah will not guide the unbelieving people. (5:67) - Shakir
Excerpt from Tafseer of Agha Mahdi Pooya1:
The followers of "Muhammad and ali Muhammad" are quite certain that this verse descended about the wilayah (regency) of Ali on the day of Ghadir Khumm, and the traditions in our records on the subject are numerous and consecutively transmitted through the Imams of the holy posterity of the Holy Prophet.
The shortest narration of the event of Ghadir is given below:
While returning from his last hajj, in 10 Hijra, the Holy Prophet, along with the huge caravan of nearly one hundred thousand Muslims, made a halt at Ghadir Khumm, a midway stop between Makka and Madina.
He had received the following verse from Allah:
O Our Messenger! Deliver what has been sent down unto you from your Lord; and if you do not, then you have not delivered His Message; and surely Allah will protect you from men. (Ma’idah, 5: 67)
The Holy Prophet mounted a tall pulpit and delivered a long sermon, recounting his services towards the fulfilment of his mission as the messenger of Allah. He asked the audience whether he had conveyed to them the commands of Allah, enumerating them one after another.
The huge gathering, in one voice, said "yes." "Do I wield authority over your souls more than you do?" He asked.
"Certainly it is so, O Messenger of Allah." They replied.
Then he asked Ali to come up. He held him in both his hands, raised him high, so much that the whole assembly of men and women saw him clearly.
He again addressed them:
O men and women! Allah is my Mawla (Lord-Master). I am the mawla of the faithfuls. I have a clear authority over their souls, And of whomsoever I am the mawla (this) Ali is his mawla. O Allah! Love him who loves Ali, hate him who hates Ali.
At the end of this declaration the following verse was revealed:
This day I have perfected for you, your religion, and have completed my favour on you, and have chosen for you Islam, as religion. (Ma’idah, 5:3)