Leviticus 21:5

Then Moses said to Aaron and to his sons Eleazar and Ithamar, “Do not uncover your heads nor tear your clothes, so that you will not die and that He will not become wrathful against all the congregation. But your relatives, the whole house of Israel, shall weep over the burning which Yahweh has brought about.

‘You shall not round off the side-growth of your heads nor harm the edges of your beard.

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

They have gone up to the temple and to Dibon, even to the high places to weep. Moab wails over Nebo and Medeba; Everyone’s head is bald and every beard is cut off.

“Now as for you, son of man, take a sharp sword; take and use it as a barber’s razor on your head and beard. Then take scales for weighing and divide the hair.

“Also they shall not shave their heads, yet they shall not let their locks grow long; they shall only trim the hair of their heads.