Leviticus 18:18-20

New Revised Standard Version Catholic Edition

¹⁸ And you shall not take^[a] a woman as a rival to her sister, uncovering her nakedness while her sister is still alive.

¹⁹ You shall not approach a woman to uncover her nakedness while she is in her menstrual uncleanness. ²⁰ You shall not have sexual relations with your kinsman’s wife, and defile yourself with her.