To start off, I'm an atheist.

My knowledge of islam is relegated to one college introduction history class about the middle east from about 500bc to the 1950's. When I consider the credibility of christianity, I think about how small of a scale jesus lived and worked in (living in 2 cities and only working with individuals known by name) and how it probably isn't true.

But muhammed, who lived, what 600 years later? managed to destroy a number of nomadic polytheist groups along the coast of saudi arabia, along with other groups. And in turn creating some kind of loosely binded empire until his death. To me, entire battles and conquests seem more verifiable and documented than a lowly individual being cured of blindness in a big city.

To me, jesus probably didn't exist because there is no reason to think he did. But muhammed may have had a large enough influence at the time to really be noticed and documented. Again, my knowledge of islam is extremely limited.