Leviticus 18:6-9

‘None of you shall approach any blood relative of his to uncover nakedness; I am the LORD. You shall not uncover the nakedness of your father, that is, the nakedness of your mother. She is your mother; you are not to uncover her nakedness. You shall not uncover the nakedness of your father’s wife; it is your father’s nakedness. The nakedness of your sister, either your father’s daughter or your mother’s daughter, whether born at home or born outside, their nakedness you shall not uncover.