Sunan Abi Dawud 4518
It was narrated from Hisham, from Qatadah, from Al-Hasan, who said:
"A free man should not be subjected to retaliation in return for a slave."
حَدَّثَنَا مُسْلِمُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا هِشَامٌ، عَنْ قَتَادَةَ، عَنِ الْحَسَنِ، قَالَ لاَ يُقَادُ الْحُرُّ بِالْعَبْدِ ‏.‏