Season 2 episode 4 (that's the 17th episode overall in the show, out of over 750 now) - titled "Two Cars in Every Garage and Three Eyes on Every Fish" features the following quote
Homer: Bart, would you like to say grace?
Bart: Dear God, we pay for all of this stuff ourselves, so thanks for nothing.
Dear God,
we pay for all of this stuff ourselves,
so thanks for nothing.
and of course pretty much the exact very short clip is on youtube so here's the link to that