Responsa for Makkot 41:3
תני תנא קמיה דרבי יוחנן על מת בין ביד בין בכלי חייב על עבודת כוכבים ביד חייב בכלי פטור והא איפכא כתיב (מלכים א יח, כח) ויתגודדו כמשפטם בחרבות וברמחים אלא אימא ביד פטור בכלי חייב:
a Tanna who taught before Rabi Yochanan: [if one made an incision/gash] for the dead, whether it was by hand or by a tool, the person is culpable [for the punishment of lashes]. If the person did it for idolatry, by hand- the person is culpable, by a tool- the person is exempt (patoor) [from the punishment of lashes]. But isn't the opposite written (I Kings 18:28): "And they gashed themselves according to their practices, with knives and spears"? Rather, one should say: if it [the incision/gash] is done by hand, one is exempt [from the punishment] but if done with a tool one is culpable.