You can't keep a good scientist down. After all, I had to come back for Einstein.
5 seconds sound clip from the Back to the Future Part III movie soundboard.
You can hear this line at 01:49:53.721 in the DVD version of the movie.
Quote context
[...]
- Doc!
- Marty!
- Meet the family. Clara, you know.
- Ma'am!
- These are our boys. Jules and Verne.
- Boys, this is Marty and Jennifer.
- Doc, I thought I'd never see you again.
- You can't keep a good scientist down. After all, I had to come back for Einstein.
- And, well, I didn't want you to be worried about me.
- Oh! I brought you a little souvenir.
- Dr. Brown, I brought this note back from the future, and now it's erased.
[...]