Musnad Ahmad 5:397

'Abdullah narrated to us, 'Ubaydullah ibn 'Umar al-Qawariri narrated to me, Yunus ibn Arqam narrated to us, Yazid ibn Abi Ziyad narrated to us, from 'Abd al-Rahman ibn Abi Layla, who said: I witnessed 'Ali in the Rahbah asking the people: I adjure by Allah any man who heard the Messenger of Allah (peace and blessings of Allah be upon him) say on the day of Ghadir Khumm: "Whoever I am his master (mawla), then 'Ali is his master," to stand and testify. 'Abd al-Rahman said: So twelve men who had participated in Badr stood up—it is as if I am looking at one of them—and they said: We testify that we heard the Messenger of Allah (peace and blessings of Allah be upon him) say on the day of Ghadir Khumm: "Am I not more worthy of the believers than their own selves, and my wives are their mothers?" We said: Yes, O Messenger of Allah. He said: "Then whoever I am his master, then 'Ali is his master. O Allah, befriend whoever befriends him, and be hostile to whoever is hostile to him."