Leviticus 21:1-6

Then the LORD said to Moses, “Speak to the priests, the sons of Aaron, and say to them: ‘ N o one shall defile himself for a dead person among his people, except for his relatives who are nearest to him, his mother and his father and his son and his daughter and his brother, also for his virgin sister, who is near to him because she has had no husband; for her he may defile himself. He shall not defile himself as a relative by marriage among his people, and so profane himself. They shall not make any baldness on their heads, nor shave off the edges of their beards, nor make any cuts in their flesh. They shall be holy to their God and not profane the name of their God, for they present the offerings by fire to the LORD, the food of their God; so they shall be holy.