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."
سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَخْطُبُ يَقُولُ مَنْ كَاتَبَ عَبْدَهُ عَلَى مِائَةِ أُوقِيَّةٍ فَأَدَّاهَا إِلاَّ عَشْرَ أَوَاقٍ أَوْ قَالَ عَشَرَةَ دَرَاهِمَ ثُمَّ عَجَزَ فَهُوَ رَقِيقٌ