2 Chronicles 23:4

Now this is what you must do, Let the third of you, the priests and Levites, come in on the sabbath, to guard the outer gates; and a third of you be at the king’s house,

Now this is the thing which ye shall do. Let a third part of you, even of the priests and of the Levites, enter in on the sabbath, even into the gates of the entrances;