Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 349
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 349, with English translation by Maimonides (Rambam).
שלא תביא אישה בהמה עליה, שנאמר "ואישה, לא תעמוד לפני בהמה לרבעה" (ויקרא יח,כג).
For a woman not to perform a sexual act with an animal, as [Leviticus 18:23] continues: "...and a woman should not present herself to an animal for sexual purposes."