She mustn't do this. She must be prevented.
4 seconds sound clip from the Forbidden Planet (1956) movie soundboard.
You can hear this line at 01:26:19 in the Blu-ray version of the movie.
Quote context
[...]
- I'm ready to go with you, darling.
- I will place him in the tractor, sir.
- She mustn't do this. She must be prevented.
- Young man, my daughter is planning a foolish action, and she'll be terribly punished.
- It's a... It's an obsolete term
[...]