Musnad Ahmad 790:114

'Abd al-Razzaq and 'Affan narrated to us—the meaning is the same, and this is the hadith of 'Abd al-Razzaq—they said: Ja'far ibn Sulayman narrated to us, he said: Yazid al-Rishk narrated to me, from Mutarrif ibn 'Abd Allah, from 'Imran ibn Husayn, who said: The Messenger of Allah (peace and blessings of Allah be upon him) sent a military detachment and appointed 'Ali ibn Abi Talib over them. He did something during his journey, and they made a pact. 'Affan said: Four of the companions of Muhammad (peace and blessings of Allah be upon him) made a pact that they would mention his matter to the Messenger of Allah (peace and blessings of Allah be upon him). 'Imran said: When we returned from a journey, we would begin with the Messenger of Allah (peace and blessings of Allah be upon him) and greet him. He said: So they entered upon him, and a man among them stood up and said: "O Messenger of Allah, 'Ali did such and such." He turned away from him. Then the second stood up and said: "O Messenger of Allah, 'Ali did such and such." He turned away from him. Then the third stood up and said: "O Messenger of Allah, 'Ali did such and such." He turned away from him. Then the fourth stood up and said: "O Messenger of Allah, 'Ali did such and such." He said: The Messenger of Allah (peace and blessings of Allah be upon him) turned toward the fourth, and his face had changed, and he said: "Leave 'Ali alone, leave 'Ali alone, leave 'Ali alone. Indeed, 'Ali is from me and I am from him, and he is the guardian (wali) of every believer after me."