Narrated 'Amr b. Shu'aib:on his father's authority, told that his grandfather reported the Prophet (ﷺ) said: A slave who has entered into an agreement to purchase his freedom is a slave as long as a dirham of the agreed price remains to be paid.
حَدَّثَنَا هَارُونُ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا أَبُو بَدْرٍ، حَدَّثَنِي أَبُو عُتْبَةَ، إِسْمَاعِيلُ بْنُ عَيَّاشٍ حَدَّثَنِي سُلَيْمَانُ بْنُ سُلَيْمٍ، عَنْ عَمْرِو بْنِ شُعَيْبٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " الْمُكَاتَبُ عَبْدٌ مَا بَقِيَ عَلَيْهِ مِنْ مُكَاتَبَتِهِ دِرْهَمٌ " .
AbuDaud
The Book of Manumission of Slaves • Hadith 3926