Leviticus 20:17, 19-20

‘If there is a man who takes his sister, his father’s daughter or his mother’s daughter, so that he sees her nakedness and she sees his nakedness, it is a disgrace; and they shall be cut off in the sight of the sons of their people. He has uncovered his sister’s nakedness; he bears his guilt.

You shall also not uncover the nakedness of your mother’s sister or of your father’s sister, for such a one has made naked his blood relative; they will bear their guilt. If there is a man who lies with his uncle’s wife he has uncovered his uncle’s nakedness; they will bear their sin. They will die childless.