Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 351
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 351, with English translation by Maimonides (Rambam).
שלא לגלות ערוות האב עצמו, שנאמר "ערוות אביך . . . לא תגלה" (ויקרא יח,ז).
Not to commit sodomy with one's father, as [Leviticus 18:7] states: "Do not commit a sexual offense with your father."