To swear by

to place great confidence in a person or thing; to trust implicitly as an authority.

See also: Swear

References in classic literature ?
Ah, I'm ready to do what you will," cried Porthos; "even to swear by Mahomet.
On the one hand, his book fulfils by elaboration his pithy summary: 'people used mainly to swear by or to but now swear mostly at': asseveration and invocation giving way to profanity and ejaculation as society moves, in his Viconian image, from the sacred to the secular phase.