Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 337
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 337, with English translation by Maimonides (Rambam).
שלא לגלות ערוות אישה ובתה, שנאמר "ערוות אישה ובתה, לא תגלה" (ויקרא יח,יז).
Not to have intimate relations with a woman and her daughter, as [Leviticus 18:17] states: "Do not commit incest [by marrying] a woman and her daughter."