Muhammad first encountered Gabriel in 610 A.D., when the first revelation from God was revealed to him. The revelations were recorded and became the Quran. Muhammad was later told to tell people to worship Allah, but was met with opposition.
Muhammad was forced to flee Mecca, which is where God’s word was revealed to him. Years later, he was able to return with his followers and was accepted. Eventually, everyone in Mecca accepted Islam, making it a holy place for Muslims around the world.