Leviticus 20:17-18

17If a man takes his sister, his father’s daughter, or his mother’s daughter, and sees her nakedness, and she his, it is a shameful thing. They are to be cut off in the sight of the children of their people, for he has uncovered his sister’s nakedness, and will bear his iniquity.

18If a man lies with a woman during her niddah and exposes her nakedness, he has exposed her flow and she has uncovered the flow of her blood. Both of them are to be cut off from among their people.