2 Chronicles 23:4-6

4This is what you shall do: One-third of you entering on the Sabbath, of the priests and the Levites, shall be keeping watch over the doors;

5one-third shall be at the king’s house; and one-third at the Gate of the Foundation. All the people shall be in the courts of the house of the Lord.

6But let no one come into the house of the Lord except the priests and those of the Levites who serve. They may go in, for they are holy; but all the people shall keep the watch of the Lord.