Musannaf Ibn Abi Shayba 13:3011

Abu Bakr narrated to us, he said: Waki' narrated to us, from Mis'ar, from Abu Hasin, from Abd al-Rahman ibn Abi Bakra, from his father, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "A judge shall not judge between two people while he is angry."