Numbers 3:1-4 (KJV)
1 These also are the generations of Aaron and Moses in the day that the Lord spake with Moses in mount Sinai.
2 And these are the names of the sons of Aaron; Nadab the firstborn, and Abihu, Eleazar, and Ithamar.
3 These are the names of the sons of Aaron, the priests which were anointed, whom he consecrated to minister in the priest’s office.
4 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.