Eddie Murphy threw a David Spade-style shot at a "Saturday Night Live" alum way back in 1981 ... making his decades-long grudge against "SNL" puzzling.

We found this clip of Murphy on "Weekend Update" during Season 6 ... talking about his fear that the military draft would return -- and then offering up the perfect draft candidate -- Garrett Morris.

Eddie then held up Morris' head shot and added, "I know he's a little over age, but word has it he's got a lot of free time right now."