1 Chronicles 24:6

Shemaiah, the scribe, wrote them before the king Their names were written and put into an urn, out of which the lots were to be drawn: which, that there might be no suspicion of fraud, were drawn before the king, the princes, the high-priest and his assistant, and before the several families of priests and Levites. One principal household being taken for Eleazar, &c. That is, one of the principal families of Eleazar was first taken, and then one of Ithamar's, and thus alternately, till all the families of Ithamar had received their lot. And afterward all the lots came forth to the rest of Eleazar's families, which were double in number to those of Ithamar.