Musannaf Ibn Abi Shayba 13:2263

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from Jabir, from ‘Ata’ ibn al-Sa’ib, from Tawus, who said: There is no harm in one saying to his mukatab (slave under a contract of manumission): "Hasten [the payment] for me, and I will remit [a portion] for you."