Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 78
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 78, with English translation by Maimonides (Rambam).
לעשר הבהמה, שנאמר: "וכל מעשר בקר וצאן" (ויקרא כז,לב).
To tithe one's herds, as [Leviticus 27:32] states: "And all the tithes of your cattle and sheep...."