Leviticus 18:6-9

“You must never have sexual relations with a close relative, for I am the LORD. “Do not violate your father by having sexual relations with your mother. She is your mother; you must not have sexual relations with her. “Do not have sexual relations with any of your father’s wives, for this would violate your father. “Do not have sexual relations with your sister or half sister, whether she is your father’s daughter or your mother’s daughter, whether she was born into your household or someone else’s.