You believe yourself to be Judge Harper, yet no one questions your sanity because you are Judge Harper.

8 seconds sound clip from the Miracle on 34th Street (1947) movie soundboard.

You can hear this line at 01:09:52 in the Blu-ray version of the movie.

Quote context

[...]

- Mr. Kringle is not sane because he believes himself to be Santa Claus.

- An entirely logical and reasonable assumption, I'm afraid.

- It would be if the clerk here or Mr. Mara or I believed that we were Santa Claus.

- Anyone who thinks he's Santa Claus is not sane.

- Not necessarily.

- You believe yourself to be Judge Harper, yet no one questions your sanity because you are Judge Harper.

- I know all about myself, young man.

- Mr. Kringle is the subject of this hearing.

- Yes, Your Honor.

- And if he is the person he believes himself to be, just as you are, then he's just as sane.

- Granted, but he isn't.

[...]