Musannaf Ibn Abi Shayba 3:3728

'Abd al-Rahman ibn Mahdi narrated to us, from Ibrahim ibn Abi Habibah, from Dawud ibn al-Husayn, from Abu Sufyan, that he used to lead the Banu 'Abd al-Ashhal in prayer while he was a *mukātab* (a slave who has a contract of manumission). Among them were men from the Companions of the Prophet, may Allah bless him and grant him peace, including Muhammad ibn Maslamah and Salamah ibn Salamah. They wanted to move him back (from leading the prayer), but when they heard his recitation, they said, "Someone like this should not be moved back."