Musannaf Ibn Abi Shayba 18:223

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, from Muhammad ibn Ishaq, from Hakim ibn Hakim, from ‘Amr ibn Shu’ayb, he said: Among what Abu Bakr and ‘Umar established regarding the judgment on wounds is: The hand, if its owner cannot eat with it, nor wrap his waist-wrapper with it, nor clean himself with it, then its full blood money (diya) is complete. Whatever is deficient [in its function] is [calculated] by proportion.