Leviticus 20:17-18

17“If a man marries his sister, the daughter of either his father or his mother, and they have sexual relations, it is a shameful disgrace. They must be publicly cut off from the community. Since the man has violated his sister, he will be punished for his sin.

18“If a man has sexual relations with a woman during her menstrual period, both of them must be cut off from the community, for together they have exposed the source of her blood flow.