Muhammad was not illiterate and wrote the Quran with his own hand.

[96:1] Read, in the name of your Lord, who created.*

[96:2] He created man from an embryo.

[96:3] Read, and your Lord, Most Exalted.

[96:4] Teaches by means of the pen.

[68:1] NuN,* the pen, and what they (the people) write.