I Chronicles 23:27-32

For by the last words of David the Levites were numbered from twenty years old and above; because their duty was to help the sons of Aaron in the service of the house of the LORD, in the courts and in the chambers, in the purifying of all holy things and the work of the service of the house of God, both with the showbread and the fine flour for the grain offering, with the unleavened cakes and what is baked in the pan, with what is mixed and with all kinds of measures and sizes; to stand every morning to thank and praise the LORD, and likewise at evening; and at every presentation of a burnt offering to the LORD on the Sabbaths and on the New Moons and on the set feasts, by number according to the ordinance governing them, regularly before the LORD; and that they should attend to the needs of the tabernacle of meeting, the needs of the holy place, and the needs of the sons of Aaron their brethren in the work of the house of the LORD.