Superstition

This is just about the greatest guest spot I've ever seen. Dude's really, really good...and then a guy who just may be the greatest living pop musician gets up with him. Phenomenal.

Of the many amazing things about this, one of the most amazing is that when it comes to the first chorus, Stevie—who has probably not had occasion to sing harmony on it since he first recorded it, roughly 10,000 performances again—immediately takes the harmony, rightly assuming that the dude wouldn't know it and would sing the melody.