Musannaf Ibn Abi Shayba 37:249

Aswad ibn Amir narrated to us, he said: Zuhayr narrated to us, he said: Abu Rawq al-Hamdani narrated to us, he said: Abu al-Ghurayf narrated to us, he said: We were the vanguard of al-Hasan ibn Ali, twelve thousand [men] at Maskin, ready to die, our swords dripping with seriousness for fighting the people of al-Sham, and over us was Abu al-Amr. He said: When the peace treaty between al-Hasan ibn Ali and Mu'awiyah reached us, it was as if our backs were broken from grief and rage. He said: When al-Hasan ibn Ali arrived in Kufa, a man from among us, whose kunya was Abu Amir, stood up to him and said: "Peace be upon you, O humiliator of the believers." He said: He replied, "Do not say that, O Abu Amir, but I disliked that I should kill them for the sake of seeking kingship or over kingship."