Musannaf Ibn Abi Shayba 3:3727

Muhammad ibn Fudayl narrated to us, from Dawud ibn Abi Hind, from Abu Nadra, from Abu Sa’id, the freed slave of Abu Usayd, who said: I got married while I was an owned slave. I invited a group of the companions of the Messenger of Allah (peace and blessings of Allah be upon him), among whom were Abu Dharr, Abu Mas’ud, and Abu Hudhayfah. The prayer was then established, and Abu Dharr stepped forward. He (Abu Sa’id) said: "Behind you!" He (Abu Dharr) turned to his companions and said: "Is it like that?" They said: "Yes." He said: "So they put me forward, and I led them in prayer while I was an owned slave."