I wouldn't kill him because he looked as frightened as I was. I looked at him and I saw myself.

10 seconds sound clip from the How to Train Your Dragon movie soundboard.

You can hear this line at 01:08:54 in the Blu-ray version of the movie.

Quote context

[...]

- I was a coward. I was weak. I wouldn't kill a dragon.

- You said wouldn't that time.

- Whatever! I wouldn't! Three hundred years, and I'm the first Viking who wouldn't kill a dragon.

- First to ride one, though.

- So?

- I wouldn't kill him because he looked as frightened as I was. I looked at him and I saw myself.

- I bet he's really frightened now.

- What are you going to do about it?

- Eh, probably something stupid.

- Good, but you've already done that.

- Then something crazy.

- That's more like it.

- Sound your positions. Stay within earshot.

- I was overhearing some of the men just now, and, well, some of them are wondering what it is we're up to here. Not me, of course.

[...]