Musannaf Ibn Abi Shayba 18:1202

Abu Bakr narrated to us, he said: Muhammad ibn Bakr narrated to us, from Ibn Jurayj, he said: 'Ata' said: "And wounds are [subject to] retaliation (qisas). It is not for the Imam to strike him, nor to imprison him; it is only the retaliation. Had Allah willed, He would have commanded imprisonment and striking; [He is] not forgetful."