How do we respond to Christians who claim that the Gospel is not corrupted and that the Qur'an was authored by humans?

The proofs of the distortion of the Torah and the Gospel are numerous, among them:

1. The writers of the Gospels were not direct disciples of Christ, but rather borrowed from Paul's atheistic and pagan ideas. The four well-known Gospels did not become known until the beginning of the third century, which raises doubts about their authenticity. 2. These Gospels have been subjected to distortion and alteration throughout history, to the extent that hardly any two versions resemble each other. As Muhammad Dia al-Azami mentioned, they have been prone to errors in transmission and intentional distortion. 3. The Gospels contain clear paganism and a distinct difference among Christian denominations regarding the divinity of Christ.

As for the established authenticity of the Qur’an and its freedom from distortion, this is indicated by several matters, including:

1. The absence of any discrepancy among its existing copies. 2. Its transmission to us by continuous, unbroken chains of narrators (Tawatur) back to the Messenger of Allah, peace and blessings be upon him. 3. It was written down during the lifetime of the Messenger of Allah, peace and blessings be upon him. 4. Allah Almighty challenged creation to produce something like the Qur’an or even a single surah from it, and this challenge remains to this day, which indicates that it is not a human composition.