1 Chronicles 23:27-32

For by the last words of David the sons of Levi were numbered from twenty years old and upward. For their duty was to assist the sons of Aaron for the service of the house of the LORD, having the care of the courts and the chambers, the cleansing of all that is holy, and any work for the service of the house of God. Their duty was also to assist with the showbread, the flour for the grain offering, the wafers of unleavened bread, the baked offering, the offering mixed with oil, and all measures of quantity or size. And they were to stand every morning, thanking and praising the LORD, and likewise at evening, and whenever burnt offerings were offered to the LORD on Sabbaths, new moons, and feast days, according to the number required of them, regularly before the LORD. Thus they were to keep charge of the tent of meeting and the sanctuary, and to attend the sons of Aaron, their brothers, for the service of the house of the LORD.