The LORD said to Moses: Speak to the priests, the sons of Aaron, and say to them: None shall defile himself for any [dead] person among his kin, except for the relatives that are closest to him: his mother, his father, his son, his daughter, and his brother; also for a virgin sister, close to him because she has not married, for her he may defile himself. But he shall not defile himselfas a kinsman by marriage, and so profane himself. They shall not shave smooth any part of their heads, or cut the side-growth of their beards, or make gashes in their flesh. They shall be holy to their God and not profane the name of their God; for they offer the LORD’s offerings by fire, the food of their God, and so must be holy. They shall not marry a woman defiled by harlotry, nor shall they marry one divorced from her husband. For they are holy to their God and you must treat them as holy, since they offer the food of your God; they shall be holy to you, for I the LORD who sanctify you am holy.
Leviticus 21:1-8