Leviticus 20:11

20:11 If a man has sexual intercourse with his father’s wife, he has exposed his father’s nakedness. Both of them must be put to death; their blood guilt is on themselves.

Leviticus 20:21

20:21 If a man has sexual intercourse with his brother’s wife, it is indecency. He has exposed his brother’s nakedness; they will be childless.