Muhammad's first revelation
In Islam, the exact date of Muhammad's first revelation is disputed, but it is generally believed by Muslims to have occurred in 610. According to Islam, while isolating at the Cave of Hira during a retreat to Jabal al-Nour near Mecca, Muhammad was visited by the angel Gabriel, who revealed to him the beginnings of what would become known as the Quran.
Source: Wikipedia — Muhammad's first revelation (CC BY-SA 4.0)