- Write another one right away, apologizing.
- But I can't.
- Why not?
- That letter was true.

7 seconds sound clip from the 'Twas the Night Before Christmas (1974) movie soundboard.

You can hear this line at 00:07:39.718 in the Blu-ray version of the movie.

Quote context

[...]

- Albert?

- Yes, Father.

- There's something we've got to talk about.

- I said, yes, Father.

- Yes, Father, what?

- I wrote the letter my friends and I, that is. All of us.

- You didn't, Albert!

- Dear Editor, Santa Claus is a fraudulent myth rooted in...

- Enough! Enough!

- Write another one right away, apologizing.

- But I can't.

- Why not?

- That letter was true.

- You don't know as much as you think, because you only think with your head. So you have a lot of trouble believing in things you can't see or touch.

- Like, for instance, what things?

- How about fairies and leprechauns on St. Patrick's Day? How about just about everything that makes a holiday gay?

- There's more to the world than meets the eye. When doubt's in your mind, give your heart a try.

[...]