It was narrated from `Ali bin Abi Talib (رضي الله عنه) that The Prophet (ﷺ) said:

`Blood money will be paid for the mukatab (a slave with a contract of manumission) commensurate with as much as he had paid off.`

حَدَّثَنَا عَفَّانُ، حَدَّثَنَا وُهَيْبٌ، حَدَّثَنَا أَيُّوبُ، عَنْ عِكْرِمَةَ، عَنْ عَلِيِّ بْنِ أَبِي طَالِبٍ، رَضِيَ اللَّهُ عَنْهُ عَنْ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ يُودَى الْمُكَاتَبُ بِقَدْرِ مَا أَدَّى‏.‏