Leviticus 21:1-3

Then the Lord said to Moses, “Speak to the priests, the sons of Aaron, and say to them: ‘No one shall defile himself for a dead person among his people,

except for his relatives who are nearest to him, his mother, his father, his son, his daughter, and his brother,

also for his virgin sister who is near to him because she has not had a husband; for her, he may defile himself.