I heard the Messenger of Allah ﷺ delivering a sermon, saying, "Whoever makes a contract with his slave to free him for one hundred ounces, and the slave pays all of it except ten ounces," or he said, "ten dirhams, and then is unable to pay the rest, he remains a slave."
حدثنا قتيبة حدثنا عبد الوارث بن سعيد عن يحيى بن أبي أنيسة
سمعت رسول الله ﷺ يخطب يقول من كاتب عبده على مائة أوقية فأداها إلا عشر أواق أو قال عشرة دراهم ثم عجز فهو رقيق
[Hasan]. Abu Dawud also reported it, Book of Manumission, chapter on the mukatab, no. 3927, and Ibn Majah, no. 2519, from the hadith of Amr bin Shuayb through this same chain, and it has corroborating narrations in Abu Dawud, no. 3926, and elsewhere.