"A sneeze is your soul trying to leave your body. Saying God Bless You shoves it back in."
I always say this as a joke. I'm pretty sure it's from the Simpsons, and not an actual historical belief. If you have any source that shows this an old wives tale or folkloric legend, I'd love to see it. That'd make it even funnier to me haha.
I think it's from "The Founder" about the guy who turned McDonald's into a national chain.