Negative commandment · Lo Ta’aseh #330 of 613
Not to have intimate relations with one's mother
שלא לגלות ערוות אם
The verse · Vayikra 18:7
עֶרְוַת אָבִיךָ וְעֶרְוַת אִמְּךָ לֹא תְגַלֵּה אִמְּךָ הִוא לֹא תְגַלֶּה עֶרְוָתָהּ
“The nakedness of thy father, or the nakedness of thy mother, shalt thou not uncover: she is thy mother; thou shalt not uncover her nakedness.”
The Rambam’s words
Not to have intimate relations with one's mother, as [Leviticus 18:7] states: "She is your mother, do not commit incest with her."
שלא לגלות ערוות אם, שנאמר "אימך היא, לא תגלה ערוותה" (ויקרא יח,ז).
Who & when
“And this prohibition is practiced in every place and at all times.”
Where in the Mishneh Torah
Hilchot Forbidden Intercourse הלכות איסורי ביאה