Numbers 8:14-16

Amplified Bible

¹⁴ “Thus you shall separate the Levites from among the Israelites, and the Levites shall be Mine [in a very special sense]. ¹⁵ Then after that the Levites may go in to serve the Tent of Meeting (tabernacle), but you shall cleanse them [first] and present them as a wave offering; ¹⁶ for they are wholly given to Me from among the Israelites. I have taken them for Myself instead of ^[a]all who are born first, the firstborn of all the Israelites.