The Prophet ﷺ said, "Whoever frees his share in a slave, the slave's full emancipation must be paid for from his wealth if he has wealth. If he has no wealth, the slave is required to work to earn the remainder of his price, without being burdened beyond his capacity."
حدثنا إسماعيل حدثنا سعيد بن أبي عروبة عن قتادة عن النضر بن أنس عن بشير بن نهيك
عن النبي ﷺ قال من أعتق شقصا له في عبد فخلاصه في ماله إن كان له مال فإن لم يكن له مال استسعي العبد غير مشقوق عليه
Its isnad is sahih. Bukhari related it, 3/182–185, in the book of dealing with wrongdoing, chapter on valuing property between partners. Muslim related it, 2/1140, no. 1503, in the book of manumission, chapter on the mention of a slave working off his freedom. Abu Dawud related it, 4/24, no. 3937. Nasai related it, 7/319, no. 4699, in the book of transactions, chapter on partnership in slaves. And Ibn Abu Shayba related it, 6/481, no. 1767.