Allah Almighty says: "And We did not teach him poetry, nor is it befitting for him." [Surah Ya-Sin: 69]
And He said: "So believe in Allah and His Messenger, the unlettered Prophet." [Surah al-A'raf: 158]
Some of the scholars of tafsir said: "The unlettered one is he who neither reads a book nor writes with his right hand."
The Shaykh (Imam al-Bayhaqi) (may Allah have mercy on him) said: "This is the view of Muqatil bin Sulayman and other scholars of tafsir."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / Q13286