Joseph and the Pyramids

Ben Carson is hardly the first person to claim the the pyramids were Joseph's granaries.  It was exceptionally common during the Middle Ages, before modern archaeology.  Jason Colavito runs down the history of the idea.  Here is what he says about the Islamic world:

The oldest Islamic attestation of the granaries myth that I know of is Al-Idrisi’s History of the Pyramids (c. 1150 CE), which was likely reporting it from a Christian source; however, I have read that earlier Islamic authors dismissed the granaries claim as unfounded. Prior to that, Islamic lore generally considered the pyramids to be antediluvian structures, or at least vastly ancient, and the storehouses to be much more recent.

The most common Islamic theory about the pyramids is actually that they were built by the prophet Idris (Enoch) as storehouses to preserve knowledge and treasure from the coming Great Flood.  The medieval Egyptians knew their contents, for we read in travel accounts that digging for treasures there was a common occupation in Cairo and its antecedents.