Musnad Abu Ya'la al-Mawsili 160:28

Abu Bakr narrated to us, Sharik narrated to us, from Abu Yazid al-Awdi, from his father, who said: Abu Hurayrah entered the mosque and the people gathered around him. A young man stood up to him and said: "I adjure you by Allah, did you hear the Messenger of Allah (peace be upon him) say: 'Whomever I am his master (mawla), then Ali is his master. O Allah, befriend whoever befriends him and be hostile to whoever is hostile to him'?" He said: So he replied, "I bear witness that I heard the Messenger of Allah (peace be upon him) say: 'Whomever I am his master (mawla), then Ali is his master. O Allah, befriend whoever befriends him and be hostile to whoever is hostile to him.'"