Au Contraire

See
www.phrases.org.uk bulletin_board 8 messages 978.html

Hi!

Thanks for the response. Actually, that article is exactly where I first saw this proverb, but that still doesn't tell me what it's origin is...

Anyone?

Thanks!
Mario.

To be brutally clear, it's a J.K. Rowling adaptation of an ancient proverb that is still with us, namely "let sleeping dogs lie", which was I believe around in much the same form in Roman times.

Yes, I think so.
The proverb "Let sleeping dogs lie" was used by Chaucer in _Troilus and Criseyde_:
"It is nought good a slepyng hound to wake."

It is also found in other European languages. For example, the Medieval French version is "N'esveillez pas lou chien qui dort."

J. K. Rowling may have changed a monosyllabic and mundane "dog" into a magical and mythical "dragon."

While not doubting the ever-resourceful Masakim's information for even a second, it's worth idly pointing out that the French, who are a contrary bunch at the best of times, have a more modern idiom, namely "ne pas reveiller le chat qui dort ", or literally "don't wake a sleeping cat".