Ran across this quote from Joseph Smith, quoted in George M. Hinkle's testimony against him in Missouri in 1839:
"I have heard Joseph Smith, jr. say that he believed Mahomet was a good man; that the Koran was not a true thing, but the world belied Mahomet, as they had belied him, and that Mahomet was a true prophet."
I wouldn't ordinarily put a lot of confidence in someone's politically motivated testimony against Joseph Smith, but this one is part of a larger pattern. Numerous individuals in 1838 and 1839 testified that Joseph had said something positive about Muhammad, or in which he identified himself with Muhammad. According to Thomas Marsh and Orson Hyde, who left the church just before the 1838 violence, Joseph Smith said that if his persecutors wouldn't leave him alone, he would become a second Muhammad and leave a trail of blood to the Pacific.
In nineteenth-century America, of course, comparing a religious leader to Muhammad was a worse slur, even, than comparing a religious leader to the Pope, which was the more politically correct way of accusing someone of unspeakable conspiracies.
From the 21st century, though, I find myself wondering what Joseph Smith actually said and whether there was a surprising degree of openness and fair-mindedness to it. Was he trying to say that early Islamic military history was not simply aggressive and coercive, but more deeply a response to bitter persecution? Did his perspective allow for important religious values to have been transmitted by God to a non-Christian faith? (Times have changed a great deal--when later LDS prophets issued a proclamation espousing such views in the 1970s, no one testified against them in court over it.) Did he simply feel a certain affinity for anyone as hated as Muhammad?
We may never know. But it seems probable that he did, in fact, say something and that several of his followers, bound too tightly in the mentality of their era's culture, grew disaffected over it. Perhaps the lesson of this incident as that we ought to be cautious not to let values from our own 21st-century culture tear us away from the values God's spirit has spoken to our souls.