2 Chronicles 23:4-6

4This is what you must do. One third of you priests and Levites who are on duty during the Sabbath will guard the doors.

5Another third of you will be stationed at the royal palace and still another third at the Foundation Gate. All the others will stand in the courtyards of the Lord’s temple.

6No one must enter the Lord’s temple except the priests and Levites who are on duty. They may enter because they are ceremonially pure. All the others should carry out their assigned service to the Lord.