LEV 18:15

15 Thou shalt not show the filthhood of thy son’s wife, for she is the wife of thy son, neither thou shalt discover her shame; and no man take his brother’s wife. (Thou shalt not uncover the nakedness of thy son’s wife, for she is thy son’s wife, so thou shalt not uncover her nakedness; and no man shall take his brother’s wife to bed.)