Numbers 3:45

ואת בהמת הלוים וגו׳ AND [THOU SHALT TAKE] THE BEASTS OF THE LEVITES [INSTEAD OF ALL THE FIRSTBORN AMONG THE BEASTS OF THE CHILDREN OF ISRAEL] — The beasts of the Levites did not redeem the firstborn of the clean beasts belonging to the Israelites, but only the first offsprings of their asses (cf. Bekhorot 4a). One lamb of the Levites (it must be remembered that for the redemption of פטר חמור a lamb is prescribed; cf. Exodus 13:13) could, however, release several first offsprings of asses belonging to Israelites. You may know that this is so, for it (Scripture) mentions the number of firstborn Israelites in excess of the number of Levites in the case of human beings, but mentions no number of firstborn animals belonging to the Israelites as being in excess over the lambs of the Levites, [although there were undoubtedly many more firstborn asses of the Israelites than ordinary lambs of the Levites] (cf. Bekhorot 4b).

קַ֣ח אֶת־הַלְוִיִּ֗ם תַּ֤חַת כׇּל־בְּכוֹר֙ בִּבְנֵ֣י יִשְׂרָאֵ֔ל וְאֶת־בֶּהֱמַ֥ת הַלְוִיִּ֖ם תַּ֣חַת בְּהֶמְתָּ֑ם וְהָיוּ־לִ֥י הַלְוִיִּ֖ם אֲנִ֥י יְהֹוָֽה׃

Take the Levites instead of all the firstborn among the children of Yisra᾽el, and the cattle of the Levites instead of their cattle; and the Levites shall be mine: I am the Lord.