Leviticus 18:6-9

‘No one shall approach any blood relative of his to uncover nakedness (have intimate relations). 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 shall not uncover her nakedness. You shall not uncover the nakedness of your father’s wife; it is your father’s nakedness. You shall not uncover the nakedness of your sister, either the daughter of your father or of your mother, whether born at home or born elsewhere.