2 Chronicles 23:4-6

4This is what you are to do: a third of you, priests and Levites who are coming on duty on the Sabbath, are to be gatekeepers.

5A third are to be at the king’s palace, and a third are to be at the Foundation Gate, and all the troops will be in the courtyards of the Lord’s temple.

6No one is to enter the Lord’s temple but the priests and those Levites who serve; they may enter because they are holy, but all the people are to obey the requirement of the Lord.