The Messenger of Allah ﷺ said, "Listen and obey, even if an Ethiopian whose head looks like a raisin is appointed over you."
حدثنا يحيى بن سعيد حدثنا شعبة حدثنا أبو التياح
قال رسول الله ﷺ اسمعوا وأطيعوا وإن استعمل عليكم حبشي كأن رأسه زبيبة
Its chain of transmission is sahih. It is found in Bukhari 1/178, in the book of adhan, chapter on the prayer led by one who commits wrongdoing, and in Muslim 3/1475, number 846, in the book of leadership, chapter on the obligation of obeying rulers, and in Bayhaqi 8/155.