Who calls the mundane world "the dust?"?

I could swear that, at some point in my comparative religion class, a tradition was mentioned in which the mundane, every-day world of the material as "the dust." I feel like this was part of a minor tradition like Zoroastrianism. Or, maybe I heard of it somewhere else. Either way, I feel the urge to go around saying it, and I'd like to be able to know where the phrase comes from so that I don't sound totally ignorant.

Thanks!