Parashas Vayikra · Aliyah 2 · Passuk 2
Chabad.org — English translation + Rashi
Torah Temima points to Menachot 18b / Toras Kohanim on ve-kamatz.
E-Daf / Tsurras Hadaf
PDF of the daf / source
English: “And he shall take a fistful” — from the taking of the fistful and onward is a duty of the priesthood.
Gezeiras hakasuv / sequence of avodos — the first mention of the kohanim with the fistful teaches that earlier steps of the minchah may be done by a non-kohen.
Pouring the oil and mixing the flour may be performed by a zar (non-kohen). From the kemitzah (fistful) onward, the avodah belongs exclusively to the kohanim.