Abd al-Rahman bin Abi Bakrah (may Allah have mercy on him) said: My father (Sayyiduna Abu Bakrah, may Allah be pleased with him) wrote, and I wrote it out with my own hand and sent it to my brother, who was in Sijistan: Let me not hear that you have judged between two men while you are angry, for I heard the Messenger of Allah (peace and blessings be upon him) say: "A judge should not judge between two men while he is angry."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20276