Musannaf Ibn Abi Shayba 13:2267

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from Jabir, from ‘Ata’, from Ibn ‘Abbas, regarding a man who says to his *mukātab* (slave under a contract of manumission): "Pay me early and I will waive [a portion] for you," [saying] there is no harm in it. Waki’ said: And Sufyan used to dislike it regarding the *mukātab* and [general] debt.