The future's already there. It's irrevocable and cannot be changed.

5 seconds sound clip from the The Time Machine (1960) movie soundboard.

You can hear this line at 00:11:19 in the Blu-ray version of the movie.

Quote context

[...]

- This is a time machine.

- All right, now you've had your little joke. Suppose you tell us what this contraption is really for.

- I've already told you, Doctor.

- The larger model can be used to carry a passenger on a journey through time. Not through space, mind you, but through time.

- If you're going to start floating about in the future, won't you gonna rather mess things up for the rest of us?

- The future's already there. It's irrevocable and cannot be changed.

- I wonder. That is the most important question to which I hope to find an answer.

- Can man control his destiny? Can he change the shape of things to come?

- Now, look here, if you've gone out of your head, I forgive you.

- But if you've made us waste all this time...

[...]