2 Chronicles 29:15, 34

They assembled their brothers, consecrated themselves, and went in to cleanse the house of the LORD, according to the commandment of the king by the words of the LORD.

But the priests were too few, so that they were unable to skin all the burnt offerings; therefore their brothers the Levites helped them until the work was completed and until the other priests had consecrated themselves. For the Levites were more conscientious to consecrate themselves than the priests.