Musannaf Ibn Abi Shayba 18:966

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Shu’bah narrated to us, he said: I asked al-Hakam and Hammad about a man who strikes a man with a stick, and he kills him. Al-Hakam said: There is no retaliation (qisas) upon him. And Hammad said: He is to be killed.