"The Messenger of Allah ruled that in the case of a Mukatab, the Diyah should be (equivalent) to the Diyah for a free man, proportionate to the amount he had paid off (towards buying his freedom)." (Dar'if)
قَضَى رَسُولُ اللَّهِ ﷺ فِي الْمُكَاتَبِ يُودَى بِقَدْرِ مَا أَدَّى مِنْ مُكَاتَبَتِهِ دِيَةَ الْحُرِّ وَمَا بَقِيَ دِيَةَ الْعَبْدِ