Leviticus 20:17-18

17If a man marries his sister, whether his father’s daughter or his mother’s daughter, and they have sexual relations, it is a disgrace. They are to be cut off publicly from their people. He has had sexual intercourse with his sister; he will bear his iniquity.

18If a man sleeps with a menstruating woman and has sexual intercourse with her, he has exposed the source of her flow, and she has uncovered the source of her blood. Both of them are to be cut off from their people.