Since the time it was revealed, Allah has preserved the Quran in the hearts of the people and in writing. It had been committed to memory by the Companions and by every generation that came after them. The care paid by the Muslims in accurately recording and memorizing the Quran has been phenomenal. Every letter and vowel mark indicating every mode of reciting the Quran has been preserved without the least addition or subtraction.
Al-Qurtubi and some other scholars of Quranic commentary mention an interesting story regarding the preservation of the Quran:
The Caliph al-Mamun used to arrange intellectual gatherings. One of these meetings was attended by a man wearing beautiful clothing, possessing a handsome face, and followed by a sweet fragrance. He spoke in a most eloquent manner. When the meeting was adjourned, al-Mamun summoned this man and asked him: “Are you from the Israelites?” He replied that he was. Al-Mamun said: “Accept Islam and I shall arrange good things for you.” Al-Mamun made him a number of promises.
The man merely replied “My religion and the religion of my forefathers” and went away. A year later, he returned as a Muslim. He spoke about matters of Islamic Law in a most proficient manner. When the meeting was adjourned, al-Mamun again summoned him and said: “Are you not the man who was with us before?” He replied that he was. Al- Mamun then asked him what had prompted him to accept Islam.
He replied: “When I left your presence, I wished to put these religions to the test. And you indeed regard me a man of keen intellect. So I turned my attention to the Torah. I produced three copies of it, each time adding and deleting some things from it. Then I took these copies to the place of prayer and they were purchased from me.
“I then turned my attention to the Gospel and drafted three copies of it, each time adding and deleting some things from it. Then I took these copies to the church and they were purchased from me.
“I then turned my attention to the Quran and drafted three copies of it, each time adding and deleting some things from it. Then I took these copies to the copyists and they skimmed through them. When they found the additions and deletions that I had made, they threw them aside and did not purchase them. So I came to know that this is a protected book, and this is the reason that I accepted Islam.”
Protected Book