Numbers 8:17

Now it happened at midnight that Yahweh struck all the firstborn in the land of Egypt, from the firstborn of Pharaoh who sat on his throne to the firstborn of the captive who was in the dungeon, and all the firstborn of cattle.

“Sanctify to Me every firstborn, the first offspring of every womb among the sons of Israel, both of man and beast; it belongs to Me.”

“Bring the tribe of Levi near and have them stand before Aaron the priest, that they may minister to him.

(as it is written in the Law of the Lord, “Every firstborn male that opens the womb shall be called holy to the Lord”),