"The facts will eventually test all our theories and they form, after all, the only impartial jury to which we can appeal." by Jean Louis Rodolphe Agassiz, 1807-1873, a famous geologist and natural historian. One thing about a book like Barlett's that, imo, surpasses the internet, is that you can see all the options laid out in front of you when you look up a word in the index.
Could your quote be a take on Sergeant Friday's "Just the facts ma'am."?