Waki reported,

Shuba said, "I came to Yahya bin al-Husayn and asked him, and he said, 'My grandmother told me that she heard the Prophet ﷺ say, while he was standing at Arafah, "If an Abyssinian slave is appointed over you, listen to him and obey him as long as he leads you by the Book of Allah the Exalted."'"

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وكيع قال

شعبة أتيت يحيى بن الحصين فسألته فقال حدثتني جدتي قالت سمعت النبي ﷺ يقول وهو واقف بعرفة إن أمر عليكم عبد حبشي فاسمعوا له وأطيعوا ما قادكم بكتاب الله تعالى