The revelation of al-Quran started in 610 CE. This event occurred in the month of Ramadan, the ninth month of the Islamic calendar. The revelation started when Prophet Muhammad, at the age of 40, received the first verses of the Quran through the Angel Gabriel while he was meditating in a cave on the outskirts of Mecca, which is now known as the Cave of Hira.
The Quran is the holy book of Islam, and its revelation to Prophet Muhammad is considered a central event in Islamic history. The revelation took place over a period of 23 years, with verses being revealed to the Prophet in various locations in and around Mecca and Medina.
In summary, the revelation of al-Quran started in 610 CE, during the month of Ramadan, when Prophet Muhammad received the first verses of the Quran through the Angel Gabriel while he was meditating in a cave in Mecca.