Musnad Ahmad 818
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، عَنْ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ يُودَى الْمُكَاتَبُ بِقَدْرِ مَا أَدَّى‏.‏