The Qur’an was written down in the lifetime of the Prophet (peace and blessings be upon him). The Prophet (peace and blessings be upon him) used to ask some of his Companions to record the verses as they were revealed. In addition to this, many of the Companions used to learn the Qur’an by heart. Thus, although the Qur’an was compiled in one volume after the Prophet’s death, it was written down during his life.
Dr. Sano Koutoub Moustapha, professor of fiqh and its principles, International Islamic University, Malaysia, states:
“We should differentiate between writing and compiling. The Holy Qur’an was compiled after the death of the Prophet (peace and blessings be upon him); that is, it was fully written and protected at the time of the Prophet and it was also fully memorized by many people at the time. In addition to that, Allah promises that He will protect this book against all forms and types of destruction and cheating. This divine promise has always been there.
Thus the Holy Qur’an is the only book which has not been subject to falsification or amendments. Furthermore, the first compilation of the Qur’an occured only less than three years after the death of the Prophet, not after ten years as your friend mentioned.
All in all, the Holy Qur’an has been proven throughout history to be an accurate and consistent book of God. All attempts to amend it or falsify its contents have failed. Yet, the Qur’an does not contain any teachings and commands that go against the nature or the interest of mankind.
Finally, do request your friend to go through the Glorious Qur’an. Surely, he will find it a wonderful and interesting book.”