Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 113
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 113, with English translation by Maimonides (Rambam).
שלא לעבוד בקודשים, שנאמר "לא תעבוד בבכור שורך" (דברים טו,יט).
Not to work with consecrated animals, as [Deuteronomy 15:19] states: "Do not work with your firstling ox."