I'm reading Quran and I'm also learning Arabic in an attempt to read Quran first-hand, without being dependent upon translations.
Recently I encountered the verse 29:48, and realized that Quran emphasizes the illiteracy of Muhammad, but relates it to the past (مِن قَبْلِهِۦ). I don't understand past of what.
From verse 96:1, I assume that it's related to before receiving revelations from Allah.
However, in this argument, it's strongly supported that Muhammad knew how to read and write. Partly because he was a merchant and we didn't have numeral systems around in those days and he had to use characters to count.
What historical evidences, other than Islamic books, do we have for literacy/illiteracy of Muhammad?