Leviticus 20:17, 19-20

‘If a man takes his sister, his father’s daughter or his mother’s daughter, and sees her nakedness and she sees his nakedness, it is a wicked thing. And they shall be cut off in the sight of their people. He has uncovered his sister’s nakedness. He shall bear his guilt.

‘You shall not uncover the nakedness of your mother’s sister nor of your father’s sister, for that would uncover his near of kin. They shall bear their guilt. 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.