Ubaidullah bin 'Umar bin Hafs عبيد الله بن عمر بن حفص بن عاصم · The Chapters on Manumission (of Slaves)

“We used to sell our slave women and the mothers of our children (Umahat Awaldina) when the Prophet (ﷺ) was still living among us, and we did not see anything wrong with that.”

“Whoever frees his share of a slave or part of his share, must pay from his wealth if he has any wealth if he has any wealth (in order to buy the rest of the slave's freedom). If he does not have wealth, then the slave should be asked to work for the price (of his freedom), without that causing him too much hardship.”