Muhammad's first revelation

Muhammad's first revelation was an event described in Islamic tradition as taking place in 610 CE, during which the Islamic prophet Muhammad was visited by the angel Jibril (Gabriel), who revealed to him the beginnings of what would later become the Qur'an. The event took place in a cave called Hira, located on the mountain Jabal An-Nour near Mecca.
Date of the Revelation
The exact date and time of the revelation is not mentioned anywhere. As a result, the exact date is disputed.
The Calendar's State During the First Revelation
To stop the calendar months from rotating through the seasons, intercalation was employed. This involved the occasional insertion of an extra month (announced at the pilgrimage), ideally seven times in nineteen years. Intercalation was said to have been introduced in 412 CE, and it was borrowed from the Jews. The Jewish official controlling the practice was known as Nasīʾ.
When the Arabs adopted the procedure they used this word nasīʾ to denote the whole system. It was operated similarly to the way the Jews operated it – the beginning of the year (Muharram) was tied to the spring season.
Identifying the Date of the First Revelation
According to Mubarak Puri, the exact date of this event was Monday, the 21st of Ramadan just before sunrise, i.e. August 10, 610 CE – when Muhammad was 40 lunar years, 6 months and 12 days of age, i.e. 39 solar years, 3 months and 22 days.
Others establish the day by projecting the fixed (i.e. non-intercalated) calendar backwards, providing a date of the night of Sunday to Monday, 13 to 14 December 610.
Summary
According to biographies of Muhammad, while on retreat in a mountain cave near Mecca (the cave of Hira), where Muhammad used to go and ponder upon the evil deeds of his community. Gabriel appears before him and commands him to "Read!". He responded, "But I cannot read!". (This happens 2 more times). Then the angel Gabriel embraced him tightly and then revealed to him the first lines of chapter 96 of the Qur'an, "Read: In the name of Allah Who created, (1) Created man from a clot. (2) Read: And Allah is the Most Generous, (3) Who taught by the pen, (4) Taught man that which he knew not.(5)" (Bukhari 4953).
Before the Revelation
Muhammad was born and raised in Mecca. When he was nearly 40, he used to spend many hours alone in prayer and speculating over the aspects of creation. He was concerned with the ignorance of divine guidance (Jahiliyyah), social unrest, injustice, widespread discrimination (particularly against women), fighting among tribes and abuse of tribal authorities prevalent in pre-Islamic Arabia. The moral degeneration of his fellow people, and his own quest for a true religion further lent fuel to this, with the result that he now began to withdraw periodically to a cave named Mount Hira, three miles north of Mecca, for contemplation and reflection. Islamic tradition holds that Muhammad during this period began to have dreams replete with spiritual significance which were fulfilled according to their true import; and this was the commencement of his divine revelation.
The First Revelation
According to Muslim tradition, during one such occasion while he was in contemplation, the angel Gabriel appeared before him in the year 610 CE and said, "Read", upon which he replied, "I am unable to read". Thereupon the angel caught hold of him and embraced him heavily. This happened two more times after which the angel commanded Muhammad to recite the following verses:
After the Revelation
Perplexed by this new experience, Muhammad made his way to home where he was consoled by his wife Khadijah, who also took him to her Nestorian Christian cousin Waraqah ibn Nawfal. Islamic tradition holds that Waraqah, upon hearing the description, testified to Muhammad's prophethood, and convinced Muhammad that the revelation was from God. Waraqah said: "O my nephew! What did you see?" When Muhammad told him what had happened to him, Waraqah replied: "This is Namus (meaning Gabriel) that Allah sent to Moses. I wish I were younger. I wish I could live up to the time when your people would turn you out." Muhammad asked: "Will they drive me out?" Waraqah answered in the affirmative and said: "Anyone who came with something similar to what you have brought was treated with hostility; and if I should be alive until that day, then I would support you strongly." A few days later Waraqah died.
The initial revelation was followed by a pause and a second encounter with Gabriel when Muhammad heard a voice from the sky and saw the same angel "sitting between the sky and the earth" and the revelations resumed with the first verses of chapter 74.
Al-Tabari and Ibn Hisham reported that Muhammad left the cave of Hira after being surprised by the revelation, but later on, returned to the cave and continued his solitude, though subsequently he returned to Mecca. Tabari and Ibn Ishaq write that Muhammad told Zubayr:
Biographers disagree about the period of time between Muhammad's first and second experiences of revelation. Ibn Ishaq writes that three years elapsed from the time that Muhammad received the first revelation until he started to preach publicly. Bukhari takes chapter 74 as the second revelation however chapter 68 has strong claims to be the second revelation.
References
Life of Muhammad
Gabriel
Angelic apparitions
Revelation