At the age of 40, while engaged in a meditative retreat, Muhammad received his first revelation from God through the Archangel Gabriel. This revelation, which continued for twenty-three years, is known as the Qur'an.
Muhammad began to recite the words he heard from Gabriel and to preach the truth which God had revealed to him. The people of Makkah were steeped in their ways of ignorance and opposed Muhammad and his small group of followers in every way. These early Muslims suffered bitter persecution.
In the year 622 CE, God gave the Muslim community the command to emigrate. This event, the hijrah or migration, in which they left Makkah for the city of Madinah, some 260 miles to the North, marks the beginning of the Muslim calendar.
Madinah provided Muhammad and the Muslims the safe and nurturing haven in which the Muslim community grew. After several years, the Prophet and his followers returned to Makkah, where they forgave their enemies and dedicated the Ka'bah to the worship of the One God. Before the Prophet died at the age of 63, the greater part of Arabia was Muslim, and within a century of his death, Islam had spread to Spain in the west and as far east as China.