Leviticus 20:17-18

17‘If a man takes his sister, his father’s daughter or his mother’s daughter, so that he sees her nakedness and she sees his nakedness, it is a disgrace; and they shall be cut off in the sight of the sons of their people. He has uncovered his sister’s nakedness; he bears [responsibility for] his guilt.

18If a man lies [intimately] with a woman during her menstrual cycle and uncovers her nakedness, he has exposed her flow, and she has uncovered the flow of her blood; both of them shall be cut off from their people [excluding them from the atonement made for them].