Sahih Bukhari: Volume 1, Book 1, Number 3:
(the mother of the faithful believers) The commencement of the Divine Inspiration to Allah's Apostle was in the form of good dreams which came true like bright day light, 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 days before his desire to see his family. He used to take with him the journey food for the stay and then come back to (his wife) Khadija to take his food like-wise 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, "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. Read! And your Lord is the Most Generous." (96.1, 96.2, 96.3) Then Allah's Apostle returned with the Inspiration and with his heart beating severely. Then he went to Khadija bint Khuwailid and said, "Cover me! Cover me!" They covered him till his fear was over and after that he told her everything that had happened and said, "I fear that something may happen to me." Khadija replied, "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."
Khadija then accompanied him to her cousin Waraqa bin Naufal bin Asad bin 'Abdul 'Uzza, who, during the PreIslamic Period became a Christian and used to write the writing with Hebrew letters. He would write from the Gospel in Hebrew as much as Allah wished him to write. He was an old man and had lost his eyesight. Khadija said to Waraqa, "Listen to the story of your nephew, O my cousin!" Waraqa asked, "O my nephew! What have you seen?" Allah's Apostle described whatever he had seen. Waraqa said, "This is the same one who keeps the secrets (angel Gabriel) whom Allah had sent to Moses. I wish I were young and could live up to the time when your people would turn you out." Allah's Apostle asked, "Will they drive me out?" Waraqa 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 Inspiration was also paused for a while.
Narrated Jabir bin 'Abdullah Al-Ansari while talking about the period of pause in revelation reporting the speech of the Prophet "While I was walking, all of a sudden I heard a voice from the sky. I looked up and saw the same angel who had visited me at the cave of Hira' sitting on a chair between the sky and the earth. I got afraid of him and came back home and said, 'Wrap me (in blankets).' And then Allah revealed the following Holy Verses (of Quran):
'O you (i.e. Muhammad)! wrapped up in garments!' Arise and warn (the people against Allah's Punishment),... up to 'and desert the idols.' (74.1-5) After this the revelation started coming strongly, frequently and regularly."
Sahih Bakhri: Volume 1, Book 1, Number 2:
(the mother of the faithful believers) Al-Harith bin Hisham asked Allah's Apostle "O Allah's Apostle! How is the Divine Inspiration revealed to you?" Allah's Apostle replied, "Sometimes it is (revealed) like the ringing of a bell, this form of Inspiration is the hardest of all and then this state passes ' off after I have grasped what is inspired. Sometimes the Angel comes in the form of a man and talks to me and I grasp whatever he says." 'Aisha added: Verily I saw the Prophet being inspired Divinely on a very cold day and noticed the Sweat dropping from his forehead (as the Inspiration was over).
From islam on line