Marty, my involvement in such a social relationship here in 1885 could result in a disruption of the space-time continuum.

9 seconds sound clip from the Back to the Future Part III movie soundboard.

You can hear this line at 00:36:01.877 in the DVD version of the movie.

Quote context

[...]

- What idiot dressed you in that outfit?

- You did.

- Shot in the back by Buford Tannen over a matter of $80, September 7? That's this Monday!

- Now I wish I'd paid him off.

- And who's this beloved Clara? I don't know anyone named Clara.

- I don't know, Doc. I thought maybe she was a girlfriend of yours.

- Marty, my involvement in such a social relationship here in 1885 could result in a disruption of the space-time continuum.

- As a scientist, I can never take that risk. Certainly not after what we've already been through.

- Emmett! Hello, Emmett.

- Hubert. It's the mayor.

- Excuse me, Emmett. Do you remember last week at the town meeting when you volunteered to meet the new schoolteacher at the station when she came in?

- Oh, yes, quite so.

- Well, we just got word she's coming in tomorrow.

[...]