2 Chronicles (Author Compiled by Isaiah and Ezra from records of Nathan, Gad, Iddo, Ahijah, Jehu and others.)
23:6`And none doth enter the house of Jehovah except the priests, and those ministering of the Levites (they go in for they are holy), and all the people keep the watch of Jehovah:
Original from The Bible Foundation - bf.org. They claim public domain status for their original text.