Sunan an-Nasa'i 4808
It was narrated that Ibn 'Abbas said:
"The Messenger of Allah ruled that the Diyah for a Mukatab who is killed should be (equivalent) to the Diyah for a free mand, proportionate to the amount be had paid off (toward buying his freedom)."
أَخْبَرَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، قَالَ حَدَّثَنَا وَكِيعٌ، قَالَ حَدَّثَنَا عَلِيُّ بْنُ الْمُبَارَكِ، عَنْ يَحْيَى، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، قَالَ قَضَى رَسُولُ اللَّهِ صلى الله عليه وسلم فِي الْمُكَاتَبِ يُقْتَلُ بِدِيَةِ الْحُرِّ عَلَى قَدْرِ مَا أَدَّى ‏.‏