1 Chronicles 24:1-4

The divisions of the descendants of Aaron were these: the sons of Aaron were Nadab, Abihu, Eleazar, and Ithamar. But Nadab and Abihu died before their father and had no sons; therefore Eleazar and Ithamar served as priests. David, with Zadok of the sons of Eleazar and Ahimelech of the sons of Ithamar, divided them according to their offices for their assigned duties. Since there were more chief men found among the descendants of Eleazar than among the descendants of Ithamar [because of Eli’s misfortunes, and Saul’s massacre of the priests at Nob], they were divided in this way: sixteen heads of fathers’ households of the descendants of Eleazar and eight of the descendants of Ithamar, corresponding to their fathers’ households.