וְאִ֗ישׁ אֲשֶׁ֨ר יִקַּ֧ח אֶת־אִשָּׁ֛ה וְאֶת־אִמָּ֖הּ זִמָּ֣ה הִ֑וא בָּאֵ֞שׁ יִשְׂרְפ֤וּ אֹתוֹ֙ וְאֶתְהֶ֔ן וְלֹא־תִהְיֶ֥ה זִמָּ֖ה בְּתוֹכְכֶֽם׃
누구든지 아내와 그 장모를 아울러 취하면 악행인즉 그와 그들을 함께 불사를지니 이는 너희 중에 악행이 없게 하려 함이니라
Akeidat Yitzchak
This prohibition is second in importance only to the wrongful taking of a life. Adultery, a common method of creating such life, is therefore prohibited on pain of death of both partners in that crime.