Musannaf Ibn Abi Shayba 13:2268

Abu Bakr narrated to us, he said: Waki' narrated to us, he said: Sufyan narrated to us, from 'Asim ibn Sulayman, from Bakr al-Muzani, from Ibn 'Umar, he said: There is no harm in a man taking goods from his mukatab (an enslaved person who has entered into a contract of manumission).