Musannaf Ibn Abi Shayba 28:1183

Waki’ narrated to us, he said: Sufyan narrated to us, from Ibrahim ibn ‘Abd al-A’la, from Suwayd ibn Ghafala, he said: ‘Umar said to me: “O Abu Umayya, I do not know, perhaps I will not meet you after this year of mine. So listen and obey, even if an Abyssinian slave with mutilated features is placed in authority over you. If he strikes you, then be patient; and if he deprives you, then be patient. And if he desires a matter that diminishes your religion, then say: ‘I hear and I obey, my blood is a sacrifice for my religion,’ but do not depart from the community.”