Abu Abdullah al-Shaybani narrates: I was sitting in the gathering of Banu al-Arqam when a man from (the tribe of) Murad came riding on his mount until he stopped at the gathering, gave the greeting of peace and asked: Is Zayd among the people? They said: Yes, this is Zayd. He said: O Zayd! I adjure you by Allah, besides whom there is no deity worthy of worship: Did you hear the Messenger of Allah (peace and blessings be upon him) saying to Ali: "Whoever I am the mawla of, Ali is his mawla. O Allah! Befriend whoever befriends him and be hostile to whoever is hostile to him"? He said: Yes. Then the man went away from him.
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5046