Let no one judge between two people while being angry.
Authentic hadithعن عبد الرحمن بن أبي بكرة قال: «كتب أبي -أو كتبتُ له- إلى ابنه عبيد الله بن أبي بَكْرَةَ وَهُوَ قَاضٍ بِسِجِسْتَانَ: أَنْ لا تَحْكُمْ بَيْنَ اثْنَيْنِ وأنت غضبان، فإني سمعت رسول الله صلى الله عليه وسلم يقول: لايحكم أحد بين اثنين وهو غضبان». وَفِي رِوَايَةٍ: «لا يَقْضِيَنَّ حَكَمٌ بين اثْنَيْنِ وهو غَضْبَانُ».
‘Abdur-Rahmān ibn Abu Bakrah reported: My father wrote, or I wrote on his behalf, to his son ‘Ubaydullāh ibn Abu Bakrah, a judge in Sijistan, saying: "Do not judge between two people while being in a state of anger, for indeed I heard the Messenger of Allah (may Allah's peace and blessings be upon him) say: 'Let no one judge between two people while being angry.'" Another narration reads: "Let no judge pass judgment between two people while being angry.”
Explanation
Allah, the Wise Lawgiver, has forbidden the judge from passing judgment between people when he is angry, for anger affects one's personal balance and probably causes him to pass unjust or wrong judgment. This would be injustice to the litigant against whom the ruling is passed and a sin and a source of regret for the judge.
Source · Narrated by Bukhari & Muslim
From the Hadith Encyclopedia (hadeethenc.com).