'Abdullah bin Umar (may Allah be pleased with them both) says: I heard the Messenger of Allah (peace and blessings of Allah be upon him) say during a sermon: "Whoever makes a contract of manumission with his slave for one hundred uqiyyah (twelve hundred dirhams), and the slave pays all except ten uqiyyah, then is unable to pay the remainder, he remains a slave."
´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.)
Maulana Ataullah Sajid
Benefits and Issues: ➊ There are many legal (shar‘i) matters in which slaves and free people differ; therefore, a person who has not yet attained complete freedom will still be subject to the rulings applicable to slaves.
➋ When a mukatab (contracted slave) completes the payment, he becomes free, and the laws applicable to free individuals will then apply to him.
Source: Commentary on Sunan Ibn Mājah by Mawlānā ‘Atā’ullāh Sājid, Page: 2519