2 Chronicles (Author Compiled by Isaiah and Ezra from records of Nathan, Gad, Iddo, Ahijah, Jehu and others.)
23:4This is the thing which ye shall do: a third part of you that come in on the sabbath, of the priests and of the Levites, shall be keepers of the doors;
Original from The Bible Foundation - bf.org. They claim public domain status for their original text.