Musnad Ahmad 318:1

'Abd al-Rahman narrated to us, he said: Sufyan narrated to us, from 'Asim—meaning Ibn 'Ubayd Allah—from 'Abd al-Rahman ibn Yazid, from his father, that the Messenger of Allah (peace and blessings of Allah be upon him) said during the Farewell Pilgrimage: "Your slaves, your slaves, your slaves. Feed them from what you eat, and clothe them from what you wear. But if they commit a sin that you do not wish to forgive, then sell the servants of Allah, and do not punish them."