The famous British historian Thomas Carlyle writes:

“One other circumstance we must not forget: that he (Muhammad) had no school-learning; of the thing we call school-learning none at all.  The art of writing was but just introduced into Arabia; it seems to be the true opinion that Muhammad never could write! Life in the Desert, with its experiences, was all his education. What of this infinite Universe he, from his dim place, with his own eyes and thoughts, could take in, so much and no more of it was he to know. Curious, if we will reflect on it, this of having no books. Except by what he could see for himself, or hear of by uncertain rumor of speech in the obscure Arabian Desert, he could know nothing. The wisdom that had been before him or at a distance from him in the world, was in a manner as good as not there for him. Of the great brother souls, flame-beacons through so many lands and times, no one directly communicates with this great soul. He is alone there, deep down in the bosom of the Wilderness; has to grow up so, — alone with Nature and his own Thoughts.””

Read an article with several quotes in Alislam.org

The featured picture is of the famous German philosopher Goethe, who was so impressed by Islam and so close that he can be called almost a Muslim. In 2011 Goethe was voted the greatest German.