Musannaf Ibn Abi Shayba 27:453

Sharik narrated to us, from Abu Ishaq, from Sa'id ibn Wahb, from Zayd ibn Yuthay', who said: It reached Ali that some people were saying things about him. He said: So he ascended the pulpit and said: "I adjure by Allah any man—and I do not adjure anyone except the companions of Muhammad, may Allah bless him and grant him peace—who heard something from the Prophet, may Allah bless him and grant him peace, to stand up." So six men stood up from the side near him, and six men stood up from the side of Sa'id ibn Wahb. They said: "We bear witness that the Messenger of Allah, may Allah bless him and grant him peace, said: 'Whoever 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.'"