A slave who has entered into an agreement to purchase his freedom remains a slave as long as a dirham of the agreed price remains to be paid
Good hadithعن عمرو بن شعيب، عن أبيه، عن جده، عن النبي صلى الله عليه وسلم قال: «المُكَاتَبُ عَبْدٌ ما بَقِيَ عليه من مُكَاتَبَتِهِ دِرْهَمٌ».
‘Amr ibn Shu‘ayb reported from his father from his grandfather that the Prophet (may Allah's peace and blessings be upon him) said: "A slave who has entered into an agreement to purchase his freedom remains a slave as long as a dirham of the agreed price remains to be paid."
Explanation
This Hadīth shows that the slave who has purchased his freedom is not manumitted and treated as a free person until he pays the agreed amount in its entirety. If he still owes a fraction of it, he remains a slave to whom the rules of slavery apply.
Source · Narrated by Abu Daoud
From the Hadith Encyclopedia (hadeethenc.com).