Musannaf Ibn Abi Shayba 18:65

Abu Bakr narrated to us, he said: Ibn ‘Ulayyah narrated to us, from Khalid, he said: ‘Umar ibn ‘Abd al-‘Aziz wrote that the *mudihah* (a wound that exposes the bone) should not exceed fifty dinars. Khalid said: He means the *mudihah* on the face.