TSK · Numbers 8:16

And thou shalt give the Levites unto Aaron and to his sons: they [are] wholly given unto him out of the children of Israel.

Because all the firstborn [are] mine; [for] on the day that I smote all the firstborn in the land of Egypt I hallowed unto me all the firstborn in Israel, both man and beast: mine shall they be: I [am] the LORD.