Not a shred of evidence

“It is a myth! It does not exist! There is not a shred of evidence that Slytherin ever built so much as a secret broom cupboard! I regret telling you such a foolish story! We will return, if you please, to history, to solid, believable, verifiable fact!”

— Professor Binns after telling the class the legend of the Chamber of Secrets (CS9: The Writing on the Wall)