You've been a good, kind, and loyal friend to me, and you made a real difference in my life.

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

You can hear this line at 00:09:37.836 in the DVD version of the movie.

Quote context

[...]

- And I fear that unnecessary time travel only risks further disruption of the space-time continuum.

- And please take care of Einstein for me. Einstein?

- He's your dog, Doc. Einstein is what you call your dog in 1985.

- I know you will give him a good home. Remember to walk him twice a day, and that he only likes canned dog food.

- These are my wishes. Please respect them and follow them.

- And so, Marty, I now say farewell and wish you Godspeed.

- You've been a good, kind, and loyal friend to me, and you made a real difference in my life.

- I will always treasure our relationship, and think on you with fond memories, warm feelings, and a special place in my heart.

- Your friend in time, Doc Emmett L. Brown. September 1st, 1885.

- I never knew I could write anything so touching.

- I know. I know, Doc. It's beautiful.

- It's all right, Copernicus. Everything is gonna be fine.

[...]