The 143rd mitzvah is that we are commanded to give the foreleg, the jaw, and the keivah1 from every kosher animal that we slaughter to a kohen.
The source of this commandment is G‑d's statement,2 "This shall be the law of what the Kohanim receive from the people when an animal is slaughtered: [whether ox or sheep you must give the Kohen the foreleg, the jaw, and the keivah]."
The details of this mitzvah are explained in the 10th chapter of tractate Chullin. Levites are not obligated in this mitzvah.3
