Negative commandment · Lo Ta’aseh #331 of 613
Not to have intimate relations with one's father's wife
שלא לגלות ערוות אשת אב
The verse · Vayikra 18:8
עֶרְוַת אֵשֶׁת־אָבִיךָ לֹא תְגַלֵּה עֶרְוַת אָבִיךָ הִוא
“The nakedness of thy father’s wife shalt thou not uncover: it is thy father’s nakedness.”
The Rambam’s words
Not to have intimate relations with one's father's wife, as [Leviticus 18:8] states: "Do not commit incest with your father's wife."
שלא לגלות ערוות אשת אב, שנאמר "ערוות אשת אביך, לא תגלה" (ויקרא יח,ח).
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