Awais Shia muslims believe that hadith indicates that the prophet was going to write a will nominating Ali ibn abi Talib as his successor, and that Omar deliberately stopped him from doing so because he did not want him coming to power. In fact the hadith is pivotal to their claim.
I know, but still, that hadith is disturbing to sunni sensibilities.
1. Muhammad could write. This will be blow to many muslims Eemaan, destroying the miracle of the Qur'an coming from an illiterate.
2. Muhammad's companions disobeyed him, prevented him from writing his will. I've heard the excuse "because Muhammad was delirious". Hasn't he been accused of being delirious before?
He (Muhammad) does not speak from desire. It is only revelation revealed.
I've used those and other ahadith, as well as other sources, to show on another forum that Muhammad could read and write. In fact, I suspect it most likely that the later generations came up with the legend that he couldn't read and write. Notice that in ahadith where Muhammad reads or write, no-one objects: "But you can't do that!"
http://debatingchristianity.com/forum/viewtopic.php?t=7227&highlight=#155434