Musannaf Ibn Abi Shayba 13:1383

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Sufyan, from Salim, from Sa’id ibn Jubayr, from Ibn ‘Umar, that he disliked for a man to remit [any part of the payment] for his mukatab (slave under a contract of manumission) until he reaches the final installment, for fear that he might become unable [to pay].