Leviticus 21:1-6

And the LORD said to Moses, “Speak to the priests, the sons of Aaron, and say to them: ‘None shall defile himself for the dead among his people, except for his relatives who are nearest to him: his mother, his father, his son, his daughter, and his brother; also his virgin sister who is near to him, who has had no husband, for her he may defile himself. Otherwise he shall not defile himself, being a chief man among his people, to profane himself. ‘They shall not make any bald place on their heads, nor shall they shave the edges of their beards nor make any cuttings in their flesh. They shall be holy to their God and not profane the name of their God, for they offer the offerings of the LORD made by fire, and the bread of their God; therefore they shall be holy.