'The Little Engine that Could'

You folks really seem to know your stuff, so maybe you can help me track down a quote: Frankly, I'm not sure whether it's from TNOTG or the roughly contemporaneous Search (I always remembered it being from TNOTG, but then I also remembered it being said by Hugh O'Brian, who was on Search, so I guess I have to be wrong about at least one).

The hero of the episode is asked by the villain why he refuses to give up. He replies: "When I was very young I read The Little Engine that Could and it had a profound effect on me."

I'd be grateful if someone could give me the proper reference. Alternatively, if there's someplace where I can download the scripts that would be great.

Thanks in advance.

Michael