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;