Leviticus 21:2-4

New Revised Standard Version, Anglicised Catholic Edition

² except for his nearest kin: his mother, his father, his son, his daughter, his brother; ³ likewise, for a virgin sister, close to him because she has had no husband, he may defile himself for her. ⁴ But he shall not defile himself as a husband among his people and so profane himself.