1 Chronicles 24:4, 31

Eleazar’s descendants were divided into sixteen groups and Ithamar’s into eight, for there were more family leaders among the descendants of Eleazar.

Like the descendants of Aaron, they were assigned to their duties by means of sacred lots, without regard to age or rank. Lots were drawn in the presence of King David, Zadok, Ahimelech, and the family leaders of the priests and the Levites.