1 Chronicles 24:5, 31

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.

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.