Muslims fast during the Ramadan in memory of the moment when Allah revealed to Muhammad the first verses of the Qur'an.
According to the Muslim beliefs, around the year 610 A.C, Muhammad went to the desert near the Mecca in order to think about his faith. Then one night, he heard a voice calling him.
And that voice came from the angel Gabriel who told Muhammad, he had been chosen to receive Allah's word. After that, for the following days, Muhammad realized he was talking to himself about the verses that should be transcribed for the Qur'an.