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.) (PT)
English reference (PT): Vol. 3, Book 19, Hadith 2519 (PT)
Arabic reference (PT): Book 19, Hadith 2615 (PT)