Supernatural, Season 2

Sam:
Dean, the angel hasn't been wrong yet! Someone's gonna do something awful, and I can stop it!

Dean:
You know, you're supposed to be bad, too, Sam. Maybe, maybe I should just stop you right now.

Sam:
You know what, Dean, I don't understand! Why can't you even consider the possibility?

Dean:
What, that this is an angel?

Sam:
Yes! Maybe we're hunting an angel here, and we should stop! Maybe this is God's will!

Dean:
Okay, all right. You know what? I get it. You've got faith. That's-hey, good for you. I'm sure it makes things easier. I'll tell you who else had faith like that -- Mom. She used to tell me when she'd tuck me in that angels were watching over us. In fact, that was the last thing she ever said to me.

Sam:
You never told me that.

Dean:
What's to tell? She was wrong. There was nothing protecting her. There's no higher power, there's no God. There's just chaos and violence and random, unpredictable evil that comes out of nowhere. It rips you to shreds. So, you want me to believe in this stuff? I'm gonna need to see some hard proof. You got any?