Numbers 3:1-4

Now these are the records of Aaron and Moses when the LORD spoke with Moses on Mount Sinai. And these are the names of the sons of Aaron: Nadab, the firstborn, and Abihu, Eleazar, and Ithamar. These are the names of the sons of Aaron, the anointed priests, whom he consecrated to minister as priests. 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.