Leviticus 20:12, 17

If a man lies with his daughter-in-law, both of them shall surely be put to death; they have committed perversion; their blood is upon them.

“If a man takes his sister, a daughter of his father or a daughter of his mother, and sees her nakedness, and she sees his nakedness, it is a disgrace, and they shall be cut off in the sight of the children of their people. He has uncovered his sister’s nakedness, and he shall bear his iniquity.