Muslims today assert that the Koran is the authentic, uncorrupted word of God. They believe that the Koran is the perfect and unchanged message received by Muhammad through God’s messenger; the Angel Gabriel.
According to the Qur’an, Islamic tradition and the biographies of Muhammad the Angel Gabriel visited Muhammad many times throughout his life and passed on to him the knowledge of the Holy Qur’an. Muhammad memorized these teachings and then shared them with his friends and family. However, Muhammad received God’s revelations in stages (Sura 25:32) and he did not write them down for he was illiterate (Sura 7:157).
When Mohammad died in 632 all that remained of the Prophets teachings were the memorizations of the Qur’ans verses by Islam’s early followers; some of which had been forgotten (Sura 2:106). Shortly after his death there was a revolt by the Arabs in some of Islam’s recently conquered lands, resulting in the Battle of Yamama. It was a costly battle in which some Muslims who were relied upon for their memorization of the Qur’an died; notably Salim whom Muhammad named as being instrumental in the spread of Qur’anic knowledge (which had still not yet been written down). “Qurra’s by the Qur’an” (people who knew the Qur’an by heart) were dying and Abu Bakr, Muhammad’s successor, feared the faith might soon be lost altogether. He ordered that, for the first time, a tangible version of the Qur’an be compiled. For this he assigned Zaid Ibn Thabit, who had been a scribe for Muhammad, the daunting task of gathering the remnants of the Qur’anic teachings. Zaid set off interviewing those who knew Muhammed and were familiar with the Qur’an, recording what could be remembered. Thus, the Qur’an became a compilation of memories. Ibn Umar (Bakr’s successor) illustrated this fact with this statement:
“Let none of you say ‘I have acquired the whole of the Qur’an.’ How does he know what all of it is when much of the Qur’an has been forgotten? Rather let him say, ‘I have acquired what has survived.’"
Over time parts of the Qur’an disappeared, both deliberately and through human error, as well as parts were added in and modified. (www.answering-islam.org/Gilchrist/Jam/index.html). Be that as it may, after Zaid’s compilation the first three caliphs Bakr, Umar and Uthman kept the authenticated Qur’an a secret until, during Uthman’s generation, quarrels began arising in the Muslim community over interpretations of Muhammad’s teachings. Uthman was pressured to reveal the Qur’an to the people. And alas it was, but once it came to the hands of the public, more disputes arose and several variants on Zaid’s Qur’an were created by those who believed his was incomplete or manipulated. Uthman however, was able to successfully stamp out these opposing views and Zaid’s Qur’an became the standard book of Islam.