Leviticus 21:4-6

Complete Jewish Bible

⁴ He may not make himself unclean, because he is a leader among his people; doing so would profane him. ⁵ Cohanim are not to make bald spots on their heads, mar the edges of their beards or cut gashes in their flesh. ⁶ Rather, they are to be holy for their God and not profane the name of their God. For they are the ones who present Adonai with offerings made by fire, the bread of their God; therefore they must be holy.