After Prophet Muhammad declared Ali ibn Abi Talib's successorship, the angel Gabriel descended with an extension of the verse Quran 5:3, adding "today I have perfected your religion for you, and I have completed my blessing upon you, and I have approved Islam as your religion", showing that there's a version of Islam that's perfected and a version that's incomplete.

After the kutba, the people were commanded to pledge allegiance to Imam Ali, and the prophet instructed them to greet him with the title Commander of the Faithful.

The Prophet instructed Ali to sit in a tent across from his own tent and ordered the Muslims to enter in groups to congratulate him and refer to him with the new title. This process took three days, and included the Muajirun, Ansar, outling Arab tribes, and the prophet's wives.

By requiring the Muslim community to personally greet Ali with the new title, the Prophet legitimized Imam Ali's position and left no room for doubt in the mind of anyone present.

Many sources say the companions of the prophet came to Imam Ali and congratulated him on the leadership. The first to address him was Umar ibn Al-Khattab, saying "O Ali, you have become my master and the master of every momin and momina"

After the three days had passed in Ghadir, a man from the tribe of Banu Makhzum (a staunch enemy of the prophet) arrived and said "O Muhammad, I wish to ask you about three matters..." and he asked if the shahadah, if the laws of islam, and if Ali's successorship was from the prophet or from Allah. When the prophet replied that they were all from Allah, the man became very angry and said "Oh Allah, if Muhammad is truthful then blast me with fire" and within minutes he was struck by lightning.

Lecture notes available at http://www.why-quran.org/?p=777.

Subscribe at http://www.why-quran.org/subscribe to watch the lectures live and participate in the Q&A at the end of each class.

Video recording of this lecture + Q&A available on YouTube at https://www.youtube.com/watch?v=S9hESB_xSZA&list=PLpkB0iwLgfTat-Pgh4W3WFmupPamiC9UT.