Narrated Aisha:

(the wife of the Prophet) The commencement (of the Divine Inspiration) to Allah's Messenger (ﷺ) was in the form of true dreams in his sleep, for he never had a dream but it turned out to be true and clear as the bright daylight. Then he began to like seclusions, so he used to go in seclusion in the cave of Hira where he used to worship Allah continuously for many nights before going back to his family to take the necessary provision (of food) for the stay. He come back to (his wife) Khadija again to take his provision (of food) likewise, till one day he received the Guidance while he was in the cave of Hira. An Angel came to him and asked him to read. Allah's Messenger (ﷺ) replied, "I do not know how to read." The Prophet (ﷺ) added, "Then the Angel held me (forcibly) and pressed me so hard that I felt distressed. Then he released me and again asked me to read, and I replied, 'I do not know how to read.' Thereupon he held me again and pressed me for the second time till I felt distressed. He then released me and asked me to read, but again I replied. 'I do not know how to read.' Thereupon he held me for the third time and pressed me till I got distressed, and then he released me and said, 'Read, in the Name of your Lord Who has created (all that exists), has created man out of a clot, Read! And your Lord is the Most Generous. Who has taught (the writing) by the pen, has taught man that which he knew not." (96.1-5). Then Allah's Messenger (ﷺ) returned with that experience; and the muscles between his neck and shoulders were trembling till he came upon Khadija (his wife) and said, "Cover me!" They covered him, and when the state of fear was over, he said to Khadija, "O Khadija! What is wrong with me? I was afraid that something bad might happen to me." Then he told her the story. Khadija said, "Nay! But receive the good tidings! By Allah, Allah will never disgrace you, for by Allah, you keep good relations with your Kith and kin, speak the truth, help the poor and the destitute, entertain your guests generously and assist those who are stricken with calamities." Khadija then took him to Waraqa bin Naufil, the son of Khadija's paternal uncle. Waraqa had been converted to Christianity in the Pre-lslamic Period and used to write Arabic and write of the Gospel in Arabic as much as Allah wished him to write. He was an old man and had lost his eyesight. Khadija said (to Waraqa), "O my cousin! Listen to what your nephew is going to say." Waraqa said, "O my nephew! What have you seen?" The Prophet (ﷺ) then described whatever he had seen. Waraqa said, "This is the same Angel (Gabriel) who was sent to Moses. I wish I were young." He added some other statement. Allah's Messenger (ﷺ) asked, "Will these people drive me out?" Waraqa said, "Yes, for nobody brought the like of what you have brought, but was treated with hostility. If I were to remain alive till your day (when you start preaching). then I would support you strongly." But a short while later Waraqa died and the Divine Inspiration was paused (stopped) for a while so that Allah's Messenger (ﷺ) was very much grieved.

A'isha, the wife of the Messenger of Allah (ﷺ), reported: The first (form) with which was started the revelation to the Messenger of Allah (ﷺ) was the true vision in sleep. And he did not see any vision but it came like the bright gleam of dawn. Thenceforth solitude became dear to him and he used to seclude himself in the cave of Hira', where he would engage in tahannuth (and that is a worship for a number of nights) before returning to his family and getting provisions again for this purpose. He would then return to Khadija and take provisions for a like period, till Truth came upon him while he was in the cave of Hira'. There came to him the angel and said: Recite, to which he replied: I am not lettered. He took hold of me [the Apostle said] and pressed me, till I was hard pressed; thereafter he let me off and said: Recite. I said: I am not lettered. He then again took hold of me and pressed me for the second time till I was hard pressed and then let me off and said: Recite, to which I replied: I am not lettered. He took hold of me and pressed me for the third time, till I was hard pressed and then let me go and said: Recite in the name of your Lord Who created, created man from a clot of blood. Recite. And your most bountiful Lord is He Who taught the use of pen, taught man what he knew not (al-Qur'an, xcvi. 1-4). Then the Prophet (ﷺ) returned therewith, his heart was trembling, and he went to Khadija and said: Wrap me up, wrap me up! So they wrapped him till the fear had left him. He then said to Khadija: O Khadija! what has happened to me? and he informed her of the happening, saying: I fear for myself. She replied: It can't be. Be happy. I swear by Allah that He shall never humiliate you. By Allah, you join ties of relationship, you speak the truth, you bear people's burden, you help the destitute, you entertain guests, and you help against the vicissitudes which affect people. Khadija then took him to Waraqa b. Naufal b. Asad b. 'Abd al-'Uzza, and he was the son of Khadija's uncle, i. e., the brother of her father. And he was the man who had embraced Christianity in the Days of Ignorance (i. e. before Islam) and he used to write books in Arabic and, therefore, wrote Injil in Arabic as God willed that he should write. He was very old and had become blind Khadija said to him: O uncle! listen to the son of your brother. Waraqa b. Naufal said: O my nephew! what did you see? The Messenger of Allah (ﷺ), then, informed him what he had seen, and Waraqa said to him: It is namus that God sent down to Musa. Would that I were then (during your prophetic career) a young man. Would that I might be alive when your people would expel you! The Messenger of Allah (ﷺ) said: Will they drive me out? Waraqa said: Yes. Never came a man with a like of what you have brought but met hostilities. If I see your day I shall help you wholeheartedly.