Musnad Ahmad 5:283

Musa ibn Dawud narrated to us, Zuhayr narrated to us, from Mansur ibn al-Mu'tamir, from Abu Ishaq, from al-Harith al-A'war, from Ali, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "If I were to appoint anyone from my Ummah as a leader without consultation, I would have appointed Ibn Umm 'Abd over them."