I heard the Messenger of Allah ﷺ say during the Farewell Pilgrimage, "Even if an Abyssinian slave were appointed over you to lead you by the Book of Allah, listen to him and obey."
أخبرنا محمد بن عبد الأعلى قال حدثنا خالد قال حدثنا شعبة عن يحيى بن حصين قال سمعت
سمعت رسول الله ﷺ يقول في حجة الوداع ولو استعمل عليكم عبد حبشي يقودكم بكتاب الله فاسمعوا له وأطيعوا
Muslim reported it in Sahih Muslim, book of Leadership, chapter on the obligation of obeying rulers in matters other than sin and its prohibition in matters of sin, hadith no. 1838, from the hadith of Shubah, with this chain, and it is in Al-Kubra, hadith no. 7815.