In The Name of Allaah, The Most Merciful, The Bestower of Mercy
Narrated Aa’isha- the Mother of the faithful believers: The commencement of the (Divine) Revelation to Allaah’s Messenger [sallal-laahu-alayhi-wasallam] was in the form of good righteous (true) dreams which came true like bright daylight, and then the love of seclusion was bestowed upon him. He used to go in seclusion in the cave of Hira’ where he used to worship (Allah Alone) continuously for many nights before returning to (or his desire to see) his family. He used to take with him- on the journey- food for the stay and then come back to (his wife) Khadeejah [radiyallaahu-anhaa] to take his food likewise again till suddenly the Truth descended upon him while he was in the cave of Hira’. The angel came to him and asked him to read. The Prophet replied, “I do not know how to read.” The Prophet added, “Then the angel caught me (forcefully) and pressed me so hard that I could not bear it any more. He then released me and again asked me to read and I replied, ‘I do not know how to read.’ Thereupon he caught me again and pressed me a second time till I could not bear it any more. He then released me and again asked me to read but again I replied, ‘I do not know how to read (or what shall I read?)’. Thereupon he caught me for the third time and pressed me, and then released me and said, ‘Read in the Name of your Lord, Who has created (all that exists). Has created man from a clot (a piece of thick coagulated blood). Read! And your Lord is the Most Generous.'” (V.96:1-3) Then Allah’s Messenger returned with the Revelation and with his heart beating severely.
Then he went to Khadeejah bint Khuwailid [radiyallaahu-anhaa] and said, “Cover me! Cover me!” They covered him till his fear was over and after that he told Khadeejah everything that had happened (and said), “I fear that something may happen to me.” Khadeejah replied, “Never! By Allaah, Allaah will never disgrace you. You keep good relations with your kith and kin, help the poor and the destitute, serve your guests generously and assist the deserving calamity-afflicted ones.” Khadeejah [radiyallaahu anhaa] then accompanied him to her cousin Waraqah bin Naufal bin Asad bin ‘Abdul ‘Uzza, who, during the Period of Ignorance became a Christian and used to write the writing with Hebrew letters. He would write from the Gospel in Hebrew as much as Allaah wished him to write. He was an old man and had lost his eyesight. Khadeejah said to Waraqah, “Listen to (the story of) your nephew, 0 my cousin!” Waraqah asked, “0 my nephew! What have you seen?” Allaah’s Messenger described whatever he had seen. Waraqah said, “This is the same one [who keeps the secrets i.e., angel Jibril (Gabriel)] whom Allah had sent to Moosaa (Moses). I wish I were young and could live up to the time when your people would turn you out.” Allah’s Messenger asked, “Will they drive me out?” Waraqah replied in the affirmative and said, “Anyone (man) who came with something similar to what you have brought was treated with hostility; and if I should remain alive till the day (when you will be turned out) then I would support you strongly.” But after a few days Waraqa died and the Divine Revelation was also paused for a while. [Saheeh Al-Bukhaari. Hadeeth Number 3]
Few Beneficial Points Extracted From This Hadeeth
 The subject matter in this hadeeth is about the beginning of the revelation, which was sent down to the Messenger [sallal-laahu-alayhi wasallam] in Ramadhaan.
 Surah Iqarah was the first part of the Qur’aan revealed to him.
 Jibreel [alayhis salaam] used to bring the revelation to him [sallal-laahu alayhi-wasallam]
 Truthfulness of the Messenger [sallal laahu alayhi wasallam] prior to being sent as a Messenger: Khadeejah said to him: ‘’Never! By Allah, Allah will never disgrace you. You keep good relations with your kith and kin, help the poor and the destitute, serve your guests generously and assist the deserving calamity-afflicted ones.”
 The revelation that was sent down to the Prophets was well known to the scholars of the people of the scripture.
 How to understand this hadeeth together with the hadeeth reported by Jaabir [radiyallaahu anhu] in which it is mentioned that Surah Al-Mud-dath-thir was the first revealed surah: What is intended in the hadeeth reported by Jaabir [radiyallaahu anhu] is that Al-Mud-dath-thir was the first Surah sent down as a command to the Messenger to warn [against Shirk, disbelief, disobedience] and call [to Tawheed, Eemaan, Islaam]. And Surah Iqrah [was the first Surah revealed to inform him that] he has been given the station of a Prophet.
 One should give concern to the subject matter regarding knowledge of the revelation, and this is proven by Aa’isha’s dedication to the subject matter regarding how the revelation began.
Source: Al-Arba’oona Hadeethaa Fee U’loomil Qur’aan…pages 5 – 8. By Shaikh Muhammad Baazmool [hafidhahullaah]. slightly paraphrased