וְאִשָּׁ֥ה אֶל־אֲחֹתָ֖הּ לֹ֣א תִקָּ֑ח לִצְרֹ֗ר לְגַלּ֧וֹת עֶרְוָתָ֛הּ עָלֶ֖יהָ בְּחַיֶּֽיהָ׃
And thou shalt not take a woman to her sister, to be a rival to her, to uncover her nakedness, beside the other in her lifetime.
Related passages and parallel verses for Leviticus 18:18.