2 Chronicles 5:11

And it came to pass, when the priests were come out of the holy place: (for all the priests that were present were sanctified, and did not then wait by course:

All the priests ... present ... did not then wait by course. The rotation system of weekly service introduced by David was intended for the ordinary duties of the priesthood; on extraordinary occasions, or when more than wonted solemnity attached to them, the priests attended in a body.