Musnad Ahmad 5:5

Abu Sa'id narrated to us, Isra'il narrated to us, Abu Ishaq narrated to us, from al-Harith, from 'Ali, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "If I were to appoint anyone as a leader without the consultation of the believers, I would have appointed Ibn Umm 'Abd."