So help you god

SO HELP YOU GOD. The formula at the end of a common oath, as administered to a witness who testifies in chief.

References in classic literature ?
Take the book in your right hand this is your name and hand- writing you swear that the contents of this your affidavit are true so help you God a shilling you must get change I haven't got it.
BEFORE YOU CAN TESTIFY HOW THE WORDS "UNDER GOD" IN THE PLEDGE IS AN UNCONSTITUTIONAL SANCTIONING OF RELIGION BT GOVERNMENT, PLEASE PLACE YOUR RIGHT HAND ON THIS BIBLE AND SWEAR THAT YOU'LL "TELL THE TRUTH, THE WHOLE TRUTH, AND NOTHING BUR THE TRUTH, SO HELP YOU GOD.