A toast to friends, was not a Robbie Burns poem. It is actually just what it says a toast to the Absent. The Person giving this toast makes this on up, and personalizes it with names of friends that are absent. He may also make it short and sweet, A Toast to Absent Friends.
I did find this one;
A Toast to Absent Friends
"to absent friends
to those we have met
to those we have yet to meet
to those who have left us for a while
and to those who have left us forever
let us lift our glasses
and drink a toast
that they may abide in our hearts
to absent friends"