Leviticus 19:28

Then Yahweh said to Moses, “Speak to the priests, the sons of Aaron, and say to them: ‘No one shall defile himself for a dead person among his people,

nor shall he approach any dead person nor defile himself even for his father or his mother;

“You are the sons of Yahweh your God; you shall not gash yourselves nor shave your forehead for the sake of the dead.

So they cried with a loud voice and gashed themselves according to their custom with swords and lances until the blood gushed out on them.