Sunan Ibn Majah 2519
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.)
حَدَّثَنَا أَبُو كُرَيْبٍ، حَدَّثَنَا عَبْدُ اللَّهِ بْنُ نُمَيْرٍ، وَمُحَمَّدُ بْنُ فُضَيْلٍ، عَنْ حَجَّاجٍ، عَنْ عَمْرِو بْنِ شُعَيْبٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏
"‏ أَيُّمَا عَبْدٍ كُوتِبَ عَلَى مِائَةِ أُوقِيَّةٍ فَأَدَّاهَا إِلاَّ عَشْرَ أُوقِيَّاتٍ فَهُوَ رَقِيقٌ ‏"‏ ‏.‏