Sunan an-Nasa'i, Volume 5, Book 45, Hadith 4813 (DarusSalam) ⓘ
It was narrated from Ibn 'Abbas that: the Prophet of Allah ruled that the Diyah for a Mukatab should be (equivalent) to the Diyah for a free man, proportionate to the amount he had paid off (toward buying his freedom).
أَخْبَرَنَا مُحَمَّدُ بْنُ عُبَيْدِ اللَّهِ بْنِ يَزِيدَ، قَالَ حَدَّثَنَا عُثْمَانُ بْنُ عَبْدِ الرَّحْمَنِ الطَّرَائِفِيُّ، قَالَ حَدَّثَنَا مُعَاوِيَةُ، عَنْ يَحْيَى بْنِ أَبِي كَثِيرٍ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ نَبِيَّ اللَّهِ صلى الله عليه وسلم قَضَى فِي الْمُكَاتَبِ أَنْ يُودَى بِقَدْرِ مَا عَتَقَ مِنْهُ دِيَةَ الْحُرِّ .
also referenced under: Hadith 4809 (Reference) & Book 45, Hadith 104 (In-Book)