Musannaf Ibn Abi Shayba 18:571

Abu Bakr narrated to us, he said: Isma'il ibn 'Ayyash narrated to us, from Ibn Jurayj, from 'Ata', who said: Retaliation (qisas) is not taken for a *ja'ifah* (a wound that reaches the body cavity), nor for a *ma'mumah* (a head wound that reaches the membrane covering the brain), nor for a *munqilah* (a wound that displaces bone), nor for anything in which there is fear for the life (of the perpetrator), nor for anything that cannot be inflicted exactly as it was inflicted upon its victim.