- You've just got to promise me you won't say a word to anybody.
- Oh, nobody but the Pentagon.

6 seconds sound clip from the The Day the Earth Stood Still (1954) classic radio play.

You can hear this line at 00:42:37 in the radio play.

Quote context

[...]

- I have got some pretty terrific news about your good friend, Mr. Carpenter.

- What about him?

- He's the man from the spaceship!

- I had that diamond, or whatever it is, checked at three different places. Nobody on earth's ever seen a stone like that!

- And after what Bobby's told us, that's enough for me!

- Why is it nobody knows about this Mr. Carpenter? Why hasn't he got any money?

- All right, Tom... it's true.

- How do you know?

- You've just got to promise me you won't say a word to anybody.

- Oh, nobody but the Pentagon.

- Are you crazy? After what happened today? He's a menace!

- You don't understand. You don't realize how important this is.

- Important? Of course it's important. And we can do something about it.

- We mustn't do anything about it, Tom. Believe me, I know what I'm talking about.

[...]