I watched this documentary, on channel 4
It was very interesting. It tried to discover if Islam was a strong motivator for the rapid expansion of the Arabic empire in the 7 th century. The presenter was seeking evidence of the influence of the prophet, whether the Islamic faith was produced as a complete entity from the outset or whether there was  evidence which was suggestive of its gradual evolution.
Now, I know very little about Islam. I have never studied the texts, although I have read an English translation of the Qur’an.
The television presenter appeared, for the camer I am sure, to be perplexed at the lack of any evidence, save the Qur’an itself.
The various experts interviewed (Western) seem to agree thtraditions an oral tradition. Indeed the presenter spent some time with Bedouin people who shared oral history with him.
The western experts were concerned that the oral tradition could not be verified and it could have been changed or manipulated. There was no written source to verify the existence birthplace or any other historic place reference in the Qur’an. The lack of documents was a problem.
The first visible representation of the Prophet was on a coin. This was the very first record of any kind in a solid form save the holy book itself. I am not so sure that I would be surprised. The Prophet was not in favour of any kind of idolatry. Christians had taken the symbol of Christ on the cross as a symbol of veneration. My understanding is that Alllah is the only God, that he and only he should be worshipped. Mosques do not have likenesses of Allah, nor of any prophet. The representation of any kind of manifestation of Allah would be a blasphemy. I understand that the words of the Qur’an appear among the decoration in a mosque, acceptable as the belief is the word came direct from Allah. Given the strong sense against portraying Allah is it really surprising that no depiction of His prophet can be found. Christ is depicted in every church, his symbol is worn by his followers and icons containing various bits and pieces of saints and items related to Christ and his disciples. This is, in my opinion, a form of idolatry. Is it surprising therefore, that the Prophet and his followers would have ensured that there was no such image of the prophet. The Western historian was frustrated by the lack of clarity over the birthplace of the prophet when viewed from the point of view of a Western historian.
The obfuscation was taken by the presenter as evidence which may or may not point to a developing religeon rather than the fully developed code in which Muslims believe. However, in my view, that obfuscation may be a clue to the truth of the claim of Islamic scholars. Forget religeon for a moment. Any figure of historical significance is hijacked by financial interests, as are mythological beings. In prehistory, we know there was some form of female goddess due to the stone carvings we have found. An idolatrous image? The are places of pilgrimage to Thomas A Beckett, the Tolpuddle martyrs have been used to generate income and provide political propaganda. Guido Fawkes beliefs have been hijacked he has been vilified and pilloried. His image is, though, well known. Boudicca is also well known and we also know how false the image of her on the embankment.
It is entirely understandable that a nomadic people with a strong oral tradition who do not have permanent structures or perhaps very few, with an abhorrence of false images would not want their belief system corrupted by idolatry. Their faith carried in their Holy book, coupled with their oral tradition, or am I mad?