Umm Husayn al-Ahmasiyyah (may Allah be pleased with her) said: I heard the Prophet (peace and blessings be upon him) saying: "Even if an Abyssinian slave is appointed as governor over you, obey him while remaining within the bounds of the Book of Allah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16600