Negative commandment · Lo Ta’aseh #340 of 613
Not to have intimate relations with one's father's sister
שלא לגלות ערוות אחות האב
The verse · Vayikra 18:12
עֶרְוַת אֲחוֹת־אָבִיךָ לֹא תְגַלֵּה שְׁאֵר אָבִיךָ הִוא
“Thou shalt not uncover the nakedness of thy father’s sister: she is thy father’s near kinswoman.”
The Rambam’s words
Not to have intimate relations with one's father's sister, as [Leviticus 18:12] states: "Do not commit incest with your father's sister."
שלא לגלות ערוות אחות האב, שנאמר "ערוות אחות אביך, לא תגלה" (ויקרא יח,יב).
Who & when
“And this prohibition is practiced in all places and at all times.”
Where in the Mishneh Torah
Hilchot Forbidden Intercourse הלכות איסורי ביאה