Narrated 'Amr bin Shu'aib:

From his father, from his grandfather that he heard the Messenger of Allah ﷺ delivering a Khutbah in which he said: "Whoever gives a writ of emancipation to his slave, for one hundred Uqiyyah, and he pays it to him less then ten Uqiyah." - or he said: "Ten Dirham" - "then he becomes incapable (of paying the remainder), the he remains a slave."

[Abu 'Eisa said:] This Hadith is Hasan Gharib. And this acted upon according to most of the people of knowledge among the Companions of the Prophet ﷺ and others: The Mukatab is a slave as long as something remains due from him for his Kitabah.

Al-Hajjaj bin Artat reported similarly from 'Amr bin Shu'aib.

حَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا عَبْدُ الْوَارِثِ بْنُ سَعِيدٍ، عَنْ يَحْيَى بْنِ أَبِي أُنَيْسَةَ، عَنْ عَمْرِو بْنِ شُعَيْبٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَخْطُبُ يَقُولُ " مَنْ كَاتَبَ عَبْدَهُ عَلَى مِائَةِ أُوقِيَّةٍ فَأَدَّاهَا إِلاَّ عَشْرَ أَوَاقٍ أَوْ قَالَ عَشَرَةَ دَرَاهِمَ ثُمَّ عَجَزَ فَهُوَ رَقِيقٌ " .

قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ غَرِيبٌ . وَالْعَمَلُ عَلَيْهِ عِنْدَ أَكْثَرِ أَهْلِ الْعِلْمِ مِنْ أَصْحَابِ النَّبِيِّ ﷺ وَغَيْرِهِمْ أَنَّ الْمُكَاتَبَ عَبْدٌ مَا بَقِيَ عَلَيْهِ شَيْءٌ مِنْ كِتَابَتِهِ . وَقَدْ رَوَى الْحَجَّاجُ بْنُ أَرْطَاةَ عَنْ عَمْرِو بْنِ شُعَيْبٍ نَحْوَهُ .