This is what I wrote in an old
thread
A couple of points to start, based purely on Islamic sources it can be said with certianty that:
1. Islamic orthodoxy emerged centuries after the rise of Islam, and before then there was much debate on the details of the prophetic biography and Quranic exegesis (Was it Isaac or Ishmael who was to be sacrificed? When was Muhammad born? etc.) Today, these issues are set in stone and agreed on by everyone, but this was not always the case.
2. Early exegetes did not know how to interpret numerous Quranic passages and offered multiple, often contradictory explanations which at times appear to be little more than guesswork.
So that 'tradition' says something today doesn't attest to its authenticity.
On the topic though, should we expect Muhammad to be illiterate by his origins?
According to tradition, before his prophetic calling he was a wealthy and successful merchant, was well travelled as a result. He was also very intelligent and widely respected for his wisdom.
We also know that numerous people in his community could read and write, so it would be slightly surprising if he was truly illiterate, although it is certainly not impossible.
Anyway, where does the belief Muhammad was illiterate come from?
In Q7:157 he is described as
al-nabi al-ummi' (you can check how this term is translated in multiple versions here
al-A`raf 7:157 and can see the diversity of persepctives: unlettered/illiterate, Ummi, gentile, layman, Arab, untutored, of the common folk, of mother wit).
So clearly it is not open and shut.
The key is the term "ummi" though, which is related to the term Ummah (community of Muslims).
Outside of the verse in question, there are no incident in the Quran of the term
ummi or related terms meaning 'illiterate'.
the Qur'anic usage of umma never indicates a 'common folk,' nor 'unlearned people' in contrast to 'learned people' or 'scholars.'
This notion is maintained by the Qur'anic ideas that each umma had its messenger (rasul),103 and
each era its sacred book.104 Only the Arabs were deprived of revelation.105 Hence, God sent a messenger from among them (wa ma arsalna min rasulin ilia hi lisani qawmihi li yubayyina lahum),106 who was chosen - as the Qur'an states - to be 'the one who warns in plain Arabic speech' 107 and to whom the 'Arabic Qur'an'108 was revealed.109 Thus the Arabs became a 'people' (umma) with a sacred text in their own language, in which they were commanded to believe.
Muḥammad, the Illiterate Prophet: An Islamic Creed in the Qur'an and Qur'anic Exegesis - S Gunther, Journal of Quranic Studies
Ibn Abbas: the term ummiyyun refers to all Arabs, i.e., those who did write and those who did not; [they were called in this way] since they were not People of the Book.
Tabari: He [it is who] sent a prophet to the ummiyyun, who was from amongst them;' [the expression 'from amongst them'] means 'from amongst the ummiyyun.' Furthermore, it is said 'from amongst them' because [Muhammad] as [an]
ummi, [i.e.] arising from the Arabs.1
[thus] the philological-historical examination of the three Qur'anic terms ummi, ummiyyun, and umma does not confirm the popular interpretation of ummi, which focuses exclusively on illiteracy.
Why did this interpretation arise then? The Quran itself acknowledges that the Unbelievers say: "These are nothing but tales of the ancients." In addition we have records of Christian apologists attacking the Quran for the same reason in the centuries after, in light of this the idea that he was illiterate becomes very theologically convenient (as Islamic theologians have noted). Thus:
this interpretation seems to reflect a post Qur'anic approach that evolved in circles of Muslim learning (possibly not before the first half of the2nd/8thcentury)123 and that has been shaped further under the influence of Muslim theologians and apologists. These findings are based on the information given in medieval Muslim sources. However, they are also supported by some medieval Christian Arabic sources
So a better fit is gentile/Arab who has not been taught the scriptures fits a lot better as 1) previous prophets (at least since Moses) had all been Jews 2) the Quran emphasises its "Arabicness" 3) it reflects a more common usage of the language in question:
...
when understood in the way shown here, the Qur’anic expression al-nabi al ummi can contribute essentially to the understanding of the history of Islam since it stresses both: the ethnic origin (Arab, Arabian), and the originality of the Prophet of Islam.125
Somewhat similar to Christianity, where God reveals Himself through Christ ('the word made flesh'), and where the virginity of the Mother of Christ, Mary, is required to produce an immaculate vessel for the Divine Word, so in Islam, God lets people know about His existence through the Qur’an. The Prophet of Islam - communicating the Word of God - came to be seen like 'a vessel that was unpolluted by 'intellectual' knowledge of word and script, so that he could carry the trust' that God had granted him through the revelation 'in perfect purity.' Muḥammad, the Illiterate Prophet
