Leviticus 20:19-21

You shall not uncover the nakedness of your mother’s sister or of your father’s sister, for that is to make naked one’s relative; they shall bear their iniquity. If a man lies with his uncle’s wife, he has uncovered his uncle’s nakedness; they shall bear their sin; they shall die childless. If a man takes his brother’s wife, it is impurity. He has uncovered his brother’s nakedness; they shall be childless.