Negative commandment · Lo Ta’aseh #352 of 613
Not to commit sodomy with one's father's brother
שלא לגלות ערוות אחי האב עצמו
The verse · Vayikra 18:14
עֶרְוַת אֲחִי־אָבִיךָ לֹא תְגַלֵּה אֶל־אִשְׁתּוֹ לֹא תִקְרָב דֹּדָתְךָ הִוא
“Thou shalt not uncover the nakedness of thy father’s brother, thou shalt not approach to his wife: she is thy aunt.”
The Rambam’s words
Not to commit sodomy with one's father's brother, as [Leviticus 18:14] states: "Do not commit a sexual offense with your father's brother."
שלא לגלות ערוות אחי האב עצמו, שנאמר "ערוות אחי אביך, לא תגלה" (ויקרא יח,יד).
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