1 Chronicles 24:1-3

The divisions of Aaron’s descendants were as follows: The sons of Aaron: Nadab, Abihu, Eleazar, and Ithamar. Nadab and Abihu died before their father did; they had no sons. Eleazar and Ithamar served as priests. David, Zadok (a descendant of Eleazar), and Ahimelech (a descendant of Ithamar) divided them into groups to carry out their assigned responsibilities.