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 not raise his voice against one of the two disputants more than he raises it against the other."
This chain contains weakness.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20459