"And you did not recite before it," meaning: before the Quran, "any book, nor did you write one with your right hand. In that case, the falsifiers would have doubted," meaning: if you had been able to read and write. And the "falsifiers," according to the interpretation of some of them, are: those who did not believe from among the People of the Book.
Muhammad said: The meaning according to this interpretation is: that they find you in their books as an unlettered person, so if you had been able to write, they would have doubted.
Surah al-Ankabut from (verse 49 - verse 52).
﴿وَمَا كُنْتَ تَتْلُو مِنْ قَبْلِهِ﴾ مِنْ قَبْلِ الْقُرْآنِ ﴿مِنْ كِتَابٍ وَلا تَخُطُّهُ بِيَمِينِكَ إِذًا لارْتَابَ المبطلون﴾ لَوْ كُنْتَ تَقْرَأُ وَتَكْتُبُ، وَ (المبطلون) فِي تَفْسِيرِ بَعْضِهِمْ: مَنْ لَمْ يُؤْمِنْ مِنْ أَهْلِ الْكِتَابِ.
قَالَ مُحَمَّدٌ: الْمَعْنَى عَلَى هَذَا التَّفْسِيرِ: أَيْ: إِنَّهُمْ يَجِدُونَكَ فِي كُتُبِهِمْ أُمِيًّا فَلَو كُنْتَ تَكْتُبُ لَارْتَابُوا.
سوررة العنكبوت من (آيَة ٤٩ - آيَة ٥٢).
