Musannaf Ibn Abi Shayba 18:275

Abu Bakr narrated to us, he said: Ibn Numayr narrated to us, from Yahya ibn Sa'id, from Sa'id ibn al-Musayyib, that Umar decreed regarding the thumb and the one next to it [the index finger] as half of the hand [diya], and regarding the middle finger as ten obligatory [camels], and the one next to it as nine obligatory [camels], and regarding the little finger as six obligatory [camels].