The Qur'an (or Koran) is the holy scripture for Muslims.
They believe it to be God's words, spoken to the Angel Gabriel and passed on to the Holy Prophet Muhammad.
There is only one version of the Qur'an and it was written in Arabic.
Muslims believe that it has not changed at all since it was first written.
The books of Hadith are said to be the narrations and actions of Muhammad, guiding Muslims on how to put the Qur'an into practice.