Prophet Muhammad was inspired but he had to express this inspiration in a human language and thus wrote down the Quran.
I go through this exact experience pretty frequently, it seems to be some sort of side effect of my bipolar (or perhaps of its being unmedicated for my entire childhood and teenage years, fuck knows how that + the abuse fucked up my brain's developing wiring). I have a lot of ideas in my brain that are pre-verbal. Most of what happens in the brain isn't in the verbal regions and you don't gain awareness of it (you don't have a verbal process telling your heart to pump blood, for example), then there is stuff that is non-verbal but you are aware of and can translate to words (like the severity of pain). I have a lot of stuff that is pre-verbal, stuff I am aware of but haven't translated into words, a lot of which makes me seem psychic when it is translated to words because I've picked up something that no one else has. It's easy for me to feel like it isn't coming from inside my head because it doesn't FEEL like it's being said by my internal monologue, it feels like external "inspiration" flooding me with information.
Some of it seems to be stuff that most humans don't have any access to. Like, for example, I can tell the sex of a fetus in the first trimester, and have even known it before the mother's first missed period. The most logical explanation for how I have known this would be that I can smell hormone changes--not something that is commonly reported in humans, but also not something that is completely impossible or even that unlikely. Something that kind of supports this theory is that people, in particular men, smell very strongly of "disgusting" to me--and this doesn't seem to be an issue with their hygiene, because I can smell it on a man (like my husband) right after he leaves the shower. I've heard other asexuals complain about this exact thing, so it's possible that it is intrinsically linked to our asexuality--perhaps we are asexual, at least in part, because sex hormones smell bad to us, and we are overly sensitive to them, so instead of finding their release arousing in a instinctive level of our brain like a normal person, we just gag.
Another thing that is similar to this is being able to "see" something on the face of a presidential candidate that allows me to know he will win the election. I first demonstrated this ability when I was 4, and it's been accurate every election since. The most logical explanation for this would be that, since some percentage of the voters are swayed by something other than a candidate's political party (otherwise every elections' results would be pretty much the same), there is something in the person--their charisma, the authority with which they carry themselves, etc.--that persuades the swing voters; and I am able to pick up on that and extrapolate it into "he'll carry the election." Again, not commonly reported, but not impossible.
Because it FEELS like this information is coming from an external source, it was easy for me as a kid to explain it by saying that I was in touch with a spirit world. In my parents' cosmology, I was a demon that had come to earth to absorb the power of their prophet/messiah figure son, so that idea fit their cosmology well. Their views didn't have much to offer me, so I was more pantheist/shamanist as a child: I believed in a spirit world, but I didn't believe that spirits were inherently good or inherently evil; they were complex individuals with complex emotions, and they could be befriended or made your enemy. I also didn't believe in a hierarchy of spirits, I believed they had a sort of general council (this was influenced by Psalm 82), and I believed in sort of patron spirits, a spirit that would individually look out for a person.
Psalm 82 is interesting from a theological perspective. The best way to explain it is to say that at the time it was written, the writer, although himself a monotheist in that he only prayed to one god, did not believe the universe was monotheistic--he believed there were other gods, but that his god was stronger than the rest of them. He had a god he worshiped as supreme, but that god was not the only god in the universe. That seems to be a pretty common theme in the Hebrew scriptures. The god in them talks a lot about being jealous and judging/punsihing other gods (not their followers--the gods themselves). This makes a lot of sense when you consider the time/place when these texts were written, and that this is not that different from what a lot of the other local tribes believed.
Here is a link to Psalm 82, as translated by a modern Jewish source:
http://www.mechon-mamre.org/p/pt/pt2682.htmBut the translation is a bit misleading, modern ideas of monotheism are being forced onto a text that doesn't really support them. What it more accurately says in verses 1 and 6-7 (the interesting verses) are: "Elohim (a plural word for god, but often used as a proper noun) stands in the place of el (the word for which elohim is a plural; again, can mean a pantheon or a proper noun)/between the elohim he judges...I have said, you are elohim, all sons of Elyon (lit. the highest, the predominant)/but, as adam (lit. mankind, man) you shall die..." and then the rest of v. 7 is weird, since Hebrew was a dead language for such a long time, the second part doesn't make a lot of sense, it's something like: first word means "in one way" (translated as down, because of the third word) second word is something like "miraculous sign" or "together" the third word is "fall" or "be cast down" so altogether it's something like "together (or, as a sign) in one direction you will fall down". (The word order is often different in Hebrew than it would be in English because they're not from the same language family, so scrambling the word order isn't necessarily wrong.)