From Sahih Muslim (Hadith 4758):
It has been narrated on the authority of Yahya b. Husain who learnt the tradition from his grandmother. She said that she heard the Prophet (ﷺ) delivering his sermon on the occasion of the Last Pilgrimage. He was saying:If a slave is appointed over you and he conducts your affairs according to the Book of Allah, you should listen to him and obeey (his orders)
Reference: Muslim 4758