Chapter 49: The Book of the Etiquette of Judges
It was narrated that 'Abdullah bin Abi Bakrah, who was a governor in Sijistan, said: "Abu Bakrah wrote to me, saying: 'I heard the Messenger of Allah [SAW] say: No one should pass two judgments on one issue, and no one should pass judgment between two disputing parties while he is angry.'"
Sunan an-Nasa'i 5421