"I heard my grandmother say: 'I heard the Messenger of Allah say, during the Farewell Pilgrimage: If an Ethiopian slave is appointed over you who rules according to the Book of Allah, then listen to him and obey."' (Using translation from Nasāʾī 4192)
سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ وَلَوْ اسْتُعْمِلَ عَلَيْكُمْ عَبْدٌ يَقُودُكُمْ بِكِتَابِ اللهِ ﷻ فَاسْمَعُوا لَهُ وَأَطِيعُوا