Part of a phrase that usually goes (after one has stated a very unbelievable story) Oh yeah? Where'd you hear that? the Quibbler? -laughs ensue- This references the newspaper The Quibbler that Xenophilius Lovegood of the Harry Potter series prints on a regular basis, which is usually full of ridiculous sightings of fictional creatures and outlandish stories.
Rutherford: Did you know that dogs go to heaven? God told me last night!
Cornelius: HA! Where'd you hear that? The Quibbler?
-laughter from all but Rutherford-