How do we respond to the statement by non-Muslims about the possibility of the Companions distorting the Holy Qur’an, given that the Prophet (peace be upon him) was illiterate?

Allah has guaranteed the preservation of the Qur’an in His saying: "Indeed, it is We who sent down the Dhikr (the Reminder) and indeed, We will be its Guardian." The Companions were upright and purified by Allah, and they were keen on collecting the Qur'an and preserving it. Their enemies, the hypocrites, did not accuse them of distorting the Book. The illiteracy of the Prophet is a miracle indicating that the Qur'an was not authored by him.