I need help, anyone know how to word a release letter??? (kinda long)

on monday I got into a fender bender, I was trying to go around a guy and I clipped his bumper-we were on the LIE stuck in massive traffic because of a dirt/sand spill thing-anyway....neither one of us wanted to go thru insurance, and there is no damage to my car-the guy called me tuesday that his mechanic can compound (??) it out for $125. I think that's an awesome price (I wouldn't really know, but it seems cheap-and I'm more than happy to pay it). So, I agreed to meet up with him and give him the money.
I wanted to have him sign something that he agrees that this is full payment and that he won;t turn around and go thru insurance-but I don't know how to word it....
does anyone have any suggestions? TIA!!!!!