Jabir ibn Abdillah ibn Harram al-Ansari, who said:
Once I came to the Prophet, peace be upon him and his progeny, and asked: "O messenger of Allah, who is your successor?" He said that the Prophet kept silent for a while, not answering me. Then he said: "O Jabir, may I not answer your question?" So I said: "My father and my mother be your ransom; By Allah, you maintained a silence, till I thought you were not pleased."
He said: "O Jabir, I was not displeased with you. I was waiting for what the heavens would reveal, and then Jibraeel came to me saying: O Muhammad, your Lord sends you salutations and says unto you: Surely, ‘Ali ibn Abi Talib is your executor and your successor over your kinsfolk and the Ummah; and a protector of your Pool (al-Hawdh). He is the bearer of your standard, preceding you into Praradise."
I said: "O Prophet of Allah! Would you say that if someone did not believe in this, I should fight him?" He said: "Yes O Jabir. This status has not been established except for being followed. So whoever follows it, he will be with me tomorrow, (i.e. on the day of Judgement) and whoever opposes it, he will never arrive near me at the Pool (al-Hawdh)."