Rick,
Since @RobPratt has already posted OR solution, I want to post another Data Step solution(no need build-in function),most likely Computer Science Student does.

%let p = 5; /* number of variables */
%let NObs = 6; /* number of observations */
data have(drop=i j);
call streaminit(123);
array x[&p];
do i = 1 to &NObs;
do j = 1 to dim(x);
x[j] = rand("Integer", -3, 9); /* SAS 9.4M4 */
end;
output;
end;
;
run;

data want;
set have;
array x{*} x1-x5;
max=.;
do i=1 to dim(x)-2;
do j=i+1 to dim(x)-1;
do k=j+1 to dim(x);
temp=x{i}*x{j}*x{k};
if temp>max then max=temp;
end;
end;
end;
drop temp i j k;
run;
proc print;run;