I strongly suspect that Ugarte left the letters of transit with Mr. Blaine.

6 seconds sound clip from the Casablanca (1942) movie soundboard.

You can hear this line at 00:51:02 in the Blu-ray version of the movie.

Quote context

[...]

- I heard a story once. As a matter of fact, I've heard a lot of stories in my time. They went along with the sound of a tinny piano playing in the parlor downstairs.

- Mister, I met a man once when I was a kid, they'd always begin.

- I guess neither one of our stories is very funny.

- Tell me who was it you left me for?

- Was it Laszlo, or were there others in between or aren't you the kind that tells?

- I strongly suspect that Ugarte left the letters of transit with Mr. Blaine.

- I would suggest you search the café immediately and thoroughly.

- If Rick has the letters, he's too smart to let you find them there.

- You give him credit for too much cleverness. My impression was he's just another blundering American.

- We mustn't underestimate American blundering. I was with them when they blundered into Berlin in 1918.

[...]