Numbers 3:4-9

Nadab and Abihu had died before the LORD when they offered profane fire before the LORD in the Wilderness of Sinai; and they had no children. So Eleazar and Ithamar ministered as priests in the presence of Aaron their father. And the LORD spoke to Moses, saying: “Bring the tribe of Levi near, and present them before Aaron the priest, that they may serve him. And they shall attend to his needs and the needs of the whole congregation before the tabernacle of meeting, to do the work of the tabernacle. Also they shall attend to all the furnishings of the tabernacle of meeting, and to the needs of the children of Israel, to do the work of the tabernacle. And you shall give the Levites to Aaron and his sons; they are given entirely to him from among the children of Israel.