Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 330
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 330, with English translation by Maimonides (Rambam).
שלא לגלות ערוות אם, שנאמר "אימך היא, לא תגלה ערוותה" (ויקרא יח,ז).
Not to have intimate relations with one's mother, as [Leviticus 18:7] states: "She is your mother, do not commit incest with her."