Sahih Bukhari
Judgments (Ahkaam)
Volume: 009 / Book Number: 089 / Hadith Number: 272
Narrated 'Abdur Rahman bin Abi Bakra:
Abu Bakra wrote to his son who was in Sijistan: 'Do not judge between two persons when you are angry, for I heard the Prophet saying, "A judge should not judge between two persons while he is in an angry mood."