Leviticus 18:6-8

⁶No one shall approach to any that is his near relation, to uncover his nakedness: I am Jehovah.

⁷The nakedness of thy father, and the nakedness of thy mother, shalt thou not uncover: she is thy mother: thou shalt not uncover her nakedness.

⁸The nakedness of thy father's wife shalt thou not uncover: it is thy father's nakedness.