What movie is this from?

I blogged before about the Flying Bean Café at the Beaconsfield train station. I loved right away this small quirky place, and one aspect of it I really love is the way they offer to give tip: by putting it in a cup that is an answer to a trivial question of culture. So as you can see on the picture, they asked what movie was the following quote: "A boy's best friend is his mother." The two choices were Forrest Gump (which I always loathed) and Psycho (classic thriller which I love so much that I actually read the novel, see this post here for details). The problem is that I had not watched either movie in a while and while I thought this sounded like Norman Bates and very, very familiar... it could be in a different context given to Gump and I could thus just be wrong and my memory was playing tricks on me. I placed my bet in the Psycho cup, only because it's my favourite movie of the two. Which one do you think it is from? And don't look down, that would be cheating.

Well, it turned out I was right! My memory and my gut feeling had not betrayed me. So it was Psycho all along. And now I am really looking forward to go back to the Flying Bean Café in Beaconsfield (or elsewhere?) to test my knowledge again. Until then, tell me if you got it right (or not) in the comments.