Exodus 34:19-20

19“The firstborn of every animal belongs to me, including the firstborn males from your herds of cattle and your flocks of sheep and goats.

20A firstborn donkey may be bought back from the Lord by presenting a lamb or young goat in its place. But if you do not buy it back, you must break its neck. However, you must buy back every firstborn son. “No one may appear before me without an offering.