Numbers 3:2-6

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 priests which were anointed, whom he consecrated to minister in the priest’s office.

And Nadab and Abihu died before the LORD, when they offered strange fire before the LORD, in the wilderness of Sinai, and they had no children: and Eleazar and Ithamar ministered in the priest’s office in the sight of Aaron their father.

And the LORD spake unto Moses, saying,

Bring the tribe of Levi near, and present them before Aaron the priest, that they may minister unto him.