Musnad Ahmad 1719

It was narrated from Hubairah: al-Hasan bin "Ali (رضي الله عنه) addressed us and said: A man [i.e., ‘Ali] left you yesterday whom none of the early ones surpassed in knowledge and none of the later ones will ever catch up with him. The Messenger of Allah (ﷺ) would send him with the banner, Jibreel on his right side and Mika"eel on his left, and he would not give up until victory was granted to him.