1 Chronicles 24:1-5

This is how Aaron’s descendants, the priests, were divided into groups for service. The sons of Aaron were Nadab, Abihu, Eleazar, and Ithamar. But Nadab and Abihu died before their father, and they had no sons. So only Eleazar and Ithamar were left to carry on as priests. With the help of Zadok, who was a descendant of Eleazar, and of Ahimelech, who was a descendant of Ithamar, David divided Aaron’s descendants into groups according to their various duties. Eleazar’s descendants were divided into sixteen groups and Ithamar’s into eight, for there were more family leaders among the descendants of Eleazar. All tasks were assigned to the various groups by means of sacred lots so that no preference would be shown, for there were many qualified officials serving God in the sanctuary from among the descendants of both Eleazar and Ithamar.