Sunan Ibn Majah Book 19, Hadith 7
the warrior in the path of Allah, the mukatab seeking to fulfill (his manumission debt), and the one getting married seeking chastity."
“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.”
“Any slave who has made a contract to buy his freedom for one hundread Uqiyyah and pays it all except ten Uqiyyah; he is still a slave.” (One Uqiyyah is equal to 40 Dirham.)