Sunan an-Nasa'i #4192 · The Book of al-Bay'ah

Sunan an-Nasa'iIt was narrated that Yahya bin Husain said
Sunan an-Nasa'i · Book 39 · The Book of al-Bay'ah
Sunan an-Nasa'i · كتاب 39 · كتاب البيعة
"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
أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، قَالَ حَدَّثَنَا خَالِدٌ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ يَحْيَى بْنِ حُصَيْنٍ، قَالَ سَمِعْتُ جَدَّتِي، تَقُولُ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ فِي حَجَّةِ الْوَدَاعِ ‏
"‏ وَلَوِ اسْتُعْمِلَ عَلَيْكُمْ عَبْدٌ حَبَشِيٌّ يَقُودُكُمْ بِكِتَابِ اللَّهِ فَاسْمَعُوا لَهُ وَأَطِيعُوا ‏"‏ ‏.‏
Reference : Sunan an-Nasa'i 4192In-book reference : Book 39, Hadith 44