Umm Salamah (may Allah be pleased with her) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever is tested with the office of judge among the people, let him be fair between them in his seating, his gestures and his glances."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20458