It wasn't Mohammed who founded Islam.

[pocaracas]

That it passed down intact and unchanged is a "mighty if", yes.

There may be sporadic variations here and there, yes, but large systematic variations are much more unlikely to occur, especially if there is a common and very basic idea that exists in at least most of the oral accounts. The idea that Muhammad claimed himself to be a prophet is something very big (and recurrent) in the oral traditions, so it's equally unlikely that someone else falsely attributed this claim of Prophethood to him at a later time without it being noticed by anyone else during that time.

I've been reading an interesting book on this subject, titled Memory in Oral Traditions: The Cognitive Psychology of Epic, Ballads, and Counting-out Rhymes. In the book, the author has carefully presented a comprehensive model - by synthesizing a multitude of empirical, theoretical, and historical research - of how oral traditions passed down through memory is more reliable than people nowadays imagine it to be. One of the conclusions is that "Oral traditions maximize memorability so that information can be stored without external memory aids for long periods of time" (p. 317). Evidently, there are many examples of ballad verses, poems, and songs produced by oral cultures in which the same basic ideas and some of the poetic structures have remained stable for centuries. The same holds for the preservation of everyday human affairs as well:

"In many situations, oral traditions provide a more appropriate model of everyday human behavior than do psychological experiments on memory. At times, people do have to remember what exactly happened on one particular occasion, as in eyewitness testimony. It is much more common, however, to abstract and remember the structure from many similar events, no one of which by itself is the best version. In general, people are better suited for the more common task (Bartlett, 1932; Neisser, 1981; Rubin, 1986)." - David C. Rubin, Memory in Oral Traditions, p. 7

"Western discourse has come to prioritize the written word as the dominant form of record keeping and until recently, Westerners have generally considered oral societies to be peoples without history. This could not be further from the truth. Oral societies record and document their histories in complex and sophisticated ways, including performative practices such as dancing and drumming. Although most oral societies, Aboriginal or otherwise, have now adopted the written word as a tool for documentation, expression and communication, many still depend on oral traditions and greatly value the oral transmission of knowledge as an intrinsic aspect of their cultures and societies."
http://indigenousfoundations.arts.ubc.ca...tions.html

"The western emphasis on textual evidence indicates an ethnocentric aversion to non-western methodology. Cultural blinders exist in many forms of historical research, like the written word, which limits the amount of knowledge a researcher can retrieve from a document. Certainly the same sort of limitations apply to different forms of textual research."
http://www.nps.gov/subjects/ugrr/discove...d-myth.htm

And how do we come to know about those muslims?
Could the source that tells us this history be skewed? Could it be exaggerating? Could it be biased?
Could it be just boosting its numbers?
Could it have found the source of the rumor?

I find those questions pretty ironic given that you yourself were so conveniently bolstering your own rumor hypothesis with weak, non-verifiable responses such as "mighty IF," "It's a possible scenario," "That is one option of how things came to be," "This is another potential way things could have unraveled, for all I know" ... and yet now you're asking me questions which I cannot possibly verify with evidence. That's a nice double-standard you have there.

You don't accept oral tradition as history, so there is no other answer to those questions that will convince you, it seems.

I'd have to go back and read a good part of the thread to remember what was going on...

But you keep missing the point where you have a wall keeping you from any original "oral tradition".
The wall of qur'an, and muslim scholars with their rules for accepting stories into the books.
And this wall may have skewed all the information of what may have happened prior to it/them.
If it did, or didn't, we can't tell.
What I can tell you is that it's very strange that:
1) such a remarkable leader would only be mentioned in writing a few years after his death;
2) Such a remarkable prophet would only be mentioned in writing (or in coins, or whatever) many years after his death.
3) Such a remarkable message would be given to a leader of a tribe whose sole means of information transmission was "oral tradition".
4) That a god, creator of the cosmos, would have one of its angels command a lost tribe in the arabian peninsula to conquer, by war, the rest of the peninsula and the world.... just so that message could be passed on to the conquered people.

Given all these strange things, I find it hard to accept that the story of that person is true.

And oral tradition is so easily broken as it can easily incorporate wonderful bits for the sake of enthralling the listener:
http://www.yale.edu/ynhti/curriculum/uni...1.x.html#g

The Folk-legend
The area of folk-legend is what Adams defines as "...a traditional, oral expression which tells of extraordinary events in the lives of everyday people, told as if it were an historical account."8 Like the folktale, folk-legend is passed on by word of mouth from generation to generation. The folk-legend tends to be ampler and more circumstantial than the folktale. The setting is very real, giving detail and local specifics to present an "aura of validity". Several authorities have compared the folktale to the novel or short story and the folk-legend to a newspaper story. The folk-legend can be conversational in tone with "give and take" between the teller and the audience. The legend is told with the assumption that the story really happened and the audience reaction revolves in part around the credibility or incredibility of the story. For instance, "The Song of Billy the Kid" begins with the words "I'll sing you a true song of Billy the Kid." This is again in contrast to the fairy tale and fable which are obviously metaphorical.

Apply to your myth of choice.