Swear not, neither by heaven, neither by the earth, neither by any other oath: but let your yea be yea; and your nay, nay.

-Bible (NewTestament)
James 5:12.

I swear to the Lord, I still can't see, Why Democracy means, Everybody but me.

-Hughes, (James Mercer) Langston
  'The Black Man Speaks'.

I've got just as much conscience as any man in business can afford to keep,öjust a little, you know, to swear by, as 't were.

-Stowe, Harriet (Elizabeth) ne¤  e Beecher
  UncleTom's Cabin, ch.1.