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 [that is, become ceremonially unclean] for the dead among his people [by touching a corpse or assisting in preparing it for burial], 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 because she has had no husband; for her he may become unclean. He shall not become unclean as a relative by marriage among his people, and so profane himself. The priests shall not shave their heads, nor shave off the edges of their beards, nor make any cuts in their body. 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.