Musannaf Ibn Abi Shayba 27:456

Sharik narrated to us, from Abu Ishaq, from Asim ibn Damra, who said: Al-Hasan ibn Ali delivered a sermon when Ali was killed. He said: "O people of Kufa, or O people of Iraq, there was among you a man who was killed tonight, or struck today, whom the predecessors did not surpass in knowledge, and the successors will not reach. When the Prophet, peace and blessings of Allah be upon him, would send him on an expedition, Gabriel would be on his right and Michael would be on his left, and he would not return until Allah granted him victory."