Numbers 3:13-15

Douay-Rheims 1899 American Edition

¹³ For every firstborn is mine: since I struck the firstborn in the land of Egypt: I have sanctified to myself whatsoever is firstborn in Israel both of man and beast, they are mine: I am the Lord.

¹⁴ And the Lord spoke to Moses in the desert of Sinai, saying:

¹⁵ Number the sons of Levi by the houses of their fathers and their families, every male from one month and upward.