Leviticus 20:19-21

19Never have sexual intercourse with your mother’s sister or your father’s sister. Whoever has sexual intercourse with a close relative must be punished.

20Whoever has sexual intercourse with his uncle’s wife violates his uncle’s marriage. That man and woman are guilty of sin. They will die without children.

21Whoever marries his brother’s wife violates his brother’s marriage and does an unclean thing. That man and woman will have no children.