The most famous is never get involved in a land war in Asia.
5 seconds sound clip from the The Princess Bride (1987) movie soundboard.
You can hear this line at 00:34:12 in the Blu-ray version of the movie.
Quote context
[...]
- You only think I guessed wrong. That's what's so funny!
- I switched glasses when your back was turned!
- You fool! You fell victim to one of the classic blunders.
- The most famous is never get involved in a land war in Asia.
- But only slightly less well known is this...
- Never go in against a Sicilian when death is on the line!
- I am no one to be trifled with. That is all you ever need know.
[...]