Since its not a direct quotation, the best match for a Nazi would be Joseph Goebbels. The quote may be a crude way of expressing Goebbels cynical views about using propaganda he knew was lies and purely manipulative. But as you can roughly see from the linked list of his famous quotes, it's rather unlike anything he exactly said in intent or rhetorical construction, so it would be an improper attribution.
I'm quite familiar with this "quote" as a common argument regarding the reason for the persistence of modern holocaust denial. I can't find who conceived of the argument first, but I doubt it comes from the Nazis themselves, since its meant as a criticism. It's difficult to determine who might be the best to attribute it to because the argument in the quote is so vague it roughly matches the ideas held by many Jewish scholars.
My best guess is this quote or argument is coming from Elie Weisel, since he is very famous. Weisel stresses a belief that the Final Solution is beyond rational understanding and must be understood mystically, since it "uniquely [among other horrific events in human history] lacked rationality-it was "evil for it's own sake"'
(Finkelstein, Norman. The Holocaust Industry.)