Musnad Abu Ya'la al-Mawsili 3:95

Ubayd Allah narrated to us, Ja'far ibn Sulayman narrated to us, Yazid al-Rishk narrated to us, from Mutarrif ibn 'Abd Allah, from 'Imran ibn Husayn, who said: The Messenger of Allah (may Allah bless him and grant him peace) sent a military detachment and appointed 'Ali ibn Abi Talib over them. He said to him: "O 'Ali, [lead] the detachment." 'Imran said: The Muslims, when they returned from a military expedition, would come to the Messenger of Allah (may Allah bless him and grant him peace) before they went to their homes, and they would inform him of their journey. He said: 'Ali had taken a slave girl. Four [men] conspired and informed him [the Prophet] of their journey. One of the four stood up and said: "O Messenger of Allah, 'Ali took a slave girl." 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, he did such and such." He said: The Messenger of Allah (may Allah bless him and grant him peace) turned, angry, with the anger recognizable on his face, and said: "What do you want from 'Ali? 'Ali is from me, and I am from him, and he is the guardian (wali) of every believer after me."