Second Book of Paralipomenon (Author Compiled by Isaias and Esdras from records of Nathan, Gad, Addo, Ahias, Jehu and others.)
36:21et conpleretur sermo Domini ex ore Hieremiae et celebraret terra sabbata sua cunctis enim diebus desolationis egit sabbatum usque dum conplerentur septuaginta anni
Original from The Bible Foundation - bf.org. They claim public domain status for their original text.