It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever is tried with judging between the Muslims, let him be just between them in his glance, his gestures, his seating and his assembly."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19926