I do vouch for the fact that I obtained the illustration from the website mentioned in the picture page, and, according to that website, it is a fifteenth century illustration of Mohammed preaching to his earliest followers. Also according to the said source ulr, the ilustration is recorded in the Manuscripts Arabe, in the Bibliotheque Nationale, Paris. The source ulr seems reliable, and it categorizes several Mohammed pictures in different groups, e.g. contemporary cartoons, Middle Ages illustrations by Muslims (it seems that there was a Persian group that allowed depicting the Prophet), Middle Ages illustrations by non-Muslims (e.g. Dante´s Inferno), etc. The illustration in question is from the group of pictures of Arab origin. Someone else has made minor corrections to the image description, but I vouch for the description online at this moment. It is my view that there is no reason to doubt the reliability of the source.