1 Chronicles 23:25-29

For David said, “The Lord God of Israel has given rest to His people, and He dwells in Jerusalem forever.

Also, the Levites will no longer need to carry the tabernacle and all its utensils for its service.”

For by the last words of David, the sons of Levi were counted from twenty years old and upward.

For their office is to assist the sons of Aaron with the service of the house of the Lord, in the courtyards and in the chambers, and in the purification of all holy things, and the work of the service of the house of God,

and with the showbread, and the fine flour for a grain offering, and unleavened wafers, or what is baked in the pan or what is well-mixed, and all measures of volume and size.