Leviticus 21:2-4

Amplified Bible

² except for his relatives who are nearest to him, his mother, his father, his son, his daughter, and his brother, ³ also his virgin sister, who is near to him because she has had no husband; for her he may become unclean. ⁴ He shall not become unclean as a relative by marriage among his people, and so profane himself.