I did some research on this quote.
It has been attributed to many.
But R G Ingersoll was first to say it.

I can honestly say I've been through
some of the most trying times an
individual can face. I've been a seeker
all my life. I finally found my truth in
The Lord Jesus Christ. I found Him when
I was in AA. I had tried everything else.
Even TM, Self Realization Fellowship
and the "Church" of Scientology. The
latter when I was 17 years old and really
didn't know any better. I've read the
Bible almost in its entirety. But what "sold"
me on Jesus was what happened
when I invited Him into my heart.
Never have I ever felt such awe,
love and pure JOY.
I KNOW THAT I KNOW THAT I KNOW.

HE'S REAL.