Mukhtasar Sahih Bukhari — Hadith 2199

Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Listen and obey (the ruler), even if an Abyssinian slave is appointed over you as your ruler, and his head is like a raisin (i.e., very small)."