Musannaf Ibn Abi Shayba 18:278

Abu Bakr narrated to us, he said: Isma'il bin Ibrahim narrated to us, from Khalid al-Hadhdha', from Abu Qilabah, from 'Amr bin Salamah, who said: 'Abd al-Malik bin Marwan wrote to us while we were with Khalid bin 'Abdullah that the fingers are [to be compensated for as] thirds. And Khalid joined the little finger and the ring finger, and the middle finger and the one next to it, and the thumb [was left] by itself.