Musnad Ahmad 5:358

'Abd al-Razzaq narrated to us, Sufyan informed us, from al-Aswad ibn Qays, from a man, from 'Ali, that he said on the Day of the Camel: "Indeed, the Messenger of Allah, may Allah bless him and grant him peace, did not entrust us with any covenant that we should take regarding leadership. Rather, it is something we saw from our own selves. Then Abu Bakr was appointed as successor—may the mercy of Allah be upon Abu Bakr—so he established [the religion] and remained upright. Then 'Umar was appointed as successor—may the mercy of Allah be upon 'Umar—so he established [the religion] and remained upright, until the religion settled firmly in its place."