Chapter 20: The Chapters on Manumission (of Slaves)
It was narrated from 'Amr bin Shu' aib, from his father, from his grandfather that the Messenger of Allah (ﷺ) said: “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.)
Sunan Ibn Majah 2519