Of questionable origins
The Canonical Origin Story
In the Name of the "Prophet"
- The Koran as we know it today could not possibly have been written at the time asserted by Islamic canon and was, in its earliest form, a Christian devotional text written in Syriac (or possibly Aramaic, they're not the same language), not Arabic;
- The earliest written, numismatic, and physical evidence for Mohammed shows not the prophet of Islam, but Jesus Christ;
- The name "Mohammed" did not exist linguistically in Arabic until well after the death of the prophet;
- Islam, at least in its earliest stages, was not a new faith but was in fact an offshoot of a heretical "reform Judaism" branch of Christianity, known as the Ebionites;
- The Koran in its current form is in fact an amalgam- and a poorly constructed one at that- of several different aspects of both Judaic and Christian tradition;
- The warrior-prophet depicted in the Medinan Suras, the (chronologically) later Suras of the Koran, is not Mohammed nor Jesus but is in fact the Biblical soldier-prophet Joshua;
- The first great wave of Islamic expansion was not Arabic but Persian in origin
The Early Physical Evidence
How, exactly, did Mohammed's parents know that he was to be the chosen one at the time of his birth, when Islamic tradition plainly states that the prophet only received the revelations at the age of 40?
The "Muhammad prophecy" of Jesus is referred to by Ibn Ishaq, Muhammad's earliest biographer, who remarked in the Gospel passage where Jesus refers to the coming of the Comforter [Aramaic Muhahhemana], he is actually referring to the coming of Muhammad. Ibn Ishaq explains: "the Munahhemana (God bless and preserve him!) in Syriac is Muhammad; in Greek he is paraclete".
The specific and extremely detailed laws laid down in the Book of Leviticus concerning marriage and adultery, homosexuality, permissible and forbidden foods, the practice of sanitary rituals, and so on and so forth, were accepted by the Ebionites completely.
The distinction here between "Nestorian" and "Ebionite" is an artificial one; the Ebionites subscribed to the Nestorian view of Christ as a man, not God made flesh, and also argued concurrently that He was an orthodox Jew, not a radical and rebel against the ancient Judaic traditions.
Mohammed, Jesus, and Joshua
In addition, it must be noted that ancient Judaism was not the quiet and self-contained faith back then that it is today. Judaism has had the ability to proselytise beaten and persecuted right out of it over the past 2,000 years- much of it, incidentally, due to the extreme damage that Islam did and continues to do to Jews. But originally, Judaism was an aggressive, even at times expansionist, faith that saw no distinction between Church and State- see, for example, Leviticus and Numbers for the laws governing both secular and religious existence, and Judges, 1st and 2nd Kings and 1st Chronicles for examples of these laws being put into action by the rulers of Canaan and Judea.
As noted above, the Ebionites accepted ancient Jewish traditions entirely, including the aggressive promotion of the faith, but also accepted Christ as a Messiah to spread that faith. It stands to reason that the figures of Jesus and Joshua could have been commingled through later revisions of past history by politically motivated rulers.