1 Chronicles 24:1-5

The divisions of the sons of Aaron were these. The sons of Aaron: Nadab, Abihu, Eleazar, and Ithamar. But Nadab and Abihu died before their father and had no children, so Eleazar and Ithamar became the priests. With the help of Zadok of the sons of Eleazar, and Ahimelech of the sons of Ithamar, David organized them according to the appointed duties in their service. Since more chief men were found among the sons of Eleazar than among the sons of Ithamar, they organized them under sixteen heads of fathers’ houses of the sons of Eleazar, and eight of the sons of Ithamar. They divided them by lot, all alike, for there were sacred officers and officers of God among both the sons of Eleazar and the sons of Ithamar.