Is Islam true?

No - and the sharpest reason isn't imported from the Gospel of John; it rises from inside the Quran itself. Repeatedly the Quran affirms the Torah and Gospel as God's own revelation - 'guidance and light' - and commands the Jews and Christians of Muhammad's day to live by the scriptures in their hands (Surah 5:47, 68). It even tells Muhammad, if he is in doubt, to 'ask those who have been reading the Scripture before you' (Surah 10:94), and insists that 'none can alter His words' (6:115).

That creates a genuine tension, what apologists call the Islamic Dilemma. The manuscript evidence - the Dead Sea Scrolls, the great fourth-century codices - shows the Bible of the seventh century is essentially the Bible we hold now. So either that Bible was already corrupted, and the Quran endorsed and consulted a corrupted book, or it was reliable, in which case it contradicts the Quran precisely where the Gospel is load-bearing: the deity of Christ, the crucifixion, and the resurrection.

The strongest Muslim reply - that the Quran stands as guardian (muhaymin) over an authentic core - addresses the corruption charge in principle. But it doesn't dissolve the dilemma: a book meant to steady the Prophet's own doubts still sends him back to the scripture in others' hands. None of this, by itself, proves Christianity; that case rests on the historical evidence for the resurrection, beginning with the early creed of 1 Corinthians 15:3-7. But the dilemma does show the Quran cannot be the flawless, final word it claims to be - which is why the honest answer here is no, a conclusion worth sharing with a friend, gently and respectfully (1 Peter 3:15).