The citation is the very first thing in the comment you responded to: The Origin of Consciousness in the Breakdown of the Bicameral Mind by Julian Jaynes. Haven't read it but heard of it many times. Interesting speculation, but there you have your citation.
You haven’t read it but you know egyptians could literally hear voices from statues? I call exaggeration :)
EDIT: I didn’t see your colon, I thought it was a period which made it sound like you were making the claim yourself, and I was eager to get resources other than his theory, only to hear his theory again lol.