The robe worn by Muhammad Ali in the leadup to his famous 1965 fight with Sonny Liston is up for auction ... and TMZ Sports has learned it's such a rare piece of boxing history, it could sell for over $500,000.
Ali donned the garment on his way to the ring in his rematch with Liston -- which many consider one of the most memorable fights ever.
Ali not only knocked out Liston in iconic fashion in the ring (you've no doubt seen the picture of the KO at this point) .