1 Chronicles 24:1-4

These were the divisions of the descendants of Aaron: The sons of Aaron were Nadab, Abihu, Eleazar and Ithamar. But Nadab and Abihu died before their father did, and they had no sons; so Eleazar and Ithamar served as the priests. With the help of Zadok a descendant of Eleazar and Ahimelek a descendant of Ithamar, David separated them into divisions for their appointed order of ministering. A larger number of leaders were found among Eleazar’s descendants than among Ithamar’s, and they were divided accordingly: sixteen heads of families from Eleazar’s descendants and eight heads of families from Ithamar’s descendants.