Musnad Ahmad 5:141

'Abdullah narrated to us, 'Ali bin Hakim al-Awdi narrated to me, Sharik informed us, from 'Uthman bin Abi Zur'ah, from Zayd bin Wahb, who said: 'Ali came to a group of people from the people of Basra, from the Khawarij, among whom was a man called al-Ja'd bin Ba'jah. He said to him: "Fear Allah, O 'Ali, for you are a dead man." 'Ali said: "Rather, I am a killed man. A strike upon this will dye this"—meaning his beard from his head—"a covenant pledged and a decree decreed, and he who fabricates has failed." He also reproached him regarding his clothing, so he said: "What do you have to do with my clothing? It is further from arrogance and more worthy for the Muslim to emulate me."