First Book of Paralipomenon (Author Compiled by Isaias and Esdras from records of Nathan, Gad, Addo, Ahias, Jehu and others.)
21:13et dixit David ad Gad ex omni parte me angustiae premunt sed melius mihi est ut incidam in manus Domini quia multae sunt miserationes eius quam in manus hominum
Original from The Bible Foundation - bf.org. They claim public domain status for their original text.