Here is an example.

The data generation process is

y=1+0.8*x+0.4*x^2 + err

err   ~ N(0,1).

*****************************************

data t1;
   do i = 1 to 50;
     x1=ranuni(12378)*4;
         x2=x1*x1;
         y=1+0.8*x1+0.4*x2+rannor(12378);
     output;
   end;
run;

proc reg data=t1;
model y=x1 x2;
plot y*(x1 x2 ) ;
plot residual.*(x1 x2 ) ;
run;
quit;