According to Abu Hanifah, the great Sunni Imam, the Qur'an is eternal in its original essence. He says, "The Qur'an is the Word of God, and is His inspired Word and Revelation. It is a necessary attribute (sifah) of God. It is not God, but still it is inseparable from God. It is written in a volume, it is read in [the Arabic] language, it is remembered in the heart, and its letters and its vowel points, and its writing are all created, for these are the works of man, but God's word is uncreated (ghairu 'l-makhluq). Its words, its writing, its letters, and its verses, are for the necessities of man, for its meaning is arrived at by their use, but the Word of God is fixed in the essence (Zat) of God, and he who says that the word of God is created is an infidel." (See Kitabu 'l- Wasiyah, p.77.) 

Muhammadans believe the Qur'an to have been written by "the hands of noble, righteous scribes," mentioned in the Suratu 'Abasa (lxxx,) 15, and to have been sent down to the lowest heaven complete, from whence it was revealed from time to time to the Prophet by the angel Gabriel. 

There is, however, only one distinct assertion in the Qur'an of Gabriel having been the medium of inspiration, namely, Suratu 'l- Baqarah (ii.), 91; and this occurs in a Medinah Surah revealed about seven years after the Prophet's rule had been established. In the Suratu 'sh-Shu'ara' (xxvi.), 193, the Qur'an is said to have been given by the Ruhu 'l-Amin, or "Faithful Spirit"; and in the Suratu 'n-Najm (liii.), 5, Muhammad claims to have been taught by the Shadidu 'l-Quwa, or "One terrible in power"; and in the Traditions the agent of inspiration is generally spoken of as "an angel" (malak)

According to the traditions, the revelation was first communicated in dreams. 'Ayishah, one of the Prophet's wives, relates (Mishkat, xxiv. 5):- 

"The first revelations which the Prophet received were in true dreams; and he never dreamt but it came to pass as regularly as the dawn of day. After this the Prophet was fond of retirement, and used to seclude himself in a cave in Mount Hira' and worship there day and night. He would, whenever he wished, return to his family at Makkah, and then go back again, tailing with him the necessaries of life. Thus he continued to return to Khadijah from time to time, until one day the revelation came down to him, and the angel (Arabic malak, Heb. malakh, "an angel; a prophet"; a name of office, not of nature [See Wilson's Hebrew Lexicon, p.181) came to him and said, ‘Read ' (iqra'); but the Prophet said, 'I am not a reader.' And the Prophet related that he (i.e. the angel) took hold of me and squeezed me as much as I could bear, and he then let me go and said again, 'Read!' And I said, 'I am not a reader.' Then he took hold of me a second time, and squeezed me as much as I could bear, and then let me go, and said, ”’Read!' And I said, 'I am not a reader.' Then he took hold of me a third time and squeezed me as much as I could bear, and said:- 

“ ‘ Read! in the name of Thy Lord who created; 
Created man from a clot of blood in the womb. 
Read for thy Lord is the most beneficent, 
He hath taught men the use of the pen; 
He hath taught man that which he knoweth not.' 

According to 'Ayishah's statement, the Suratu 'l-'Alaq (xcvi.) was the first portion of the Qur'an revealed; but it is more probable that the poetical Surahs, in which there is no express declaration of the prophetic office, or of a divine commission, were composed at an earlier period. Internal evidence would assign the earliest date to the Surahs az-Zalzalah (xcix.), al-'Asr (ciii.), al-'Adiyat (c.), and al-Fatihah (i.), which are rather the utterances of a searcher after truth than of an Apostle of God. Although the Qur’an now appears as one book, the Muslim admits that it was not all made known to the Prophet in one and the same manner. 
 

Mr. Sell, in his Faith of Islam, quoting from the Mudariju 'n-Nubuwah, p. 509, gives the following as some of the modes of inspiration :- 
 

" 1. It is recorded on the authority of 'A'ye-sha, one of Muhammad's wives, that a brightness like the brightness of the morning came upon the Prophet. According to some commentators, this brightness remained six months. In some mysterious way Gabriel, through this brightness or vision, made known the will of God. 
 

"2. Gabriel appeared in the form of Dahiah (Dahyah), one of the Companions of the Prophet, renowned for his beauty and gracefulness. A learned dispute has arisen with regard to the abode of the soul of Gabriel when he assumed the bodily form of Dahiah. At times, the angelic nature of Gabriel overcame Muhammad, who was then translated to the world of angels. This always happened when the revelation was one of bad news, such as denunciations or predictions of woe. At other times, when the message brought by Gabriel was one of consolation and comfort, the human nature of the Prophet overcame the angelic nature of the angel, who, in such case, having assumed a human form, proceeded to deliver the message. 

"3. The Prophet heard at times the noise of the tinkling of a bell. To him alone was known the meaning of the sound. He alone could distinguish in, and through it, the words which Gabriel wished him to understand. The effect of this mode of Wahl (Wahy) was more marvellous than that of any of the other ways. When his ear caught the sound his whole frame became agitated. On the coldest day, the perspiration, like beads of silver, would roll down his face. The glorious brightness of his countenance gave place to a ghastly hue, whilst the way in which he bent down his head showed the intensity of the emotion through which he was passing. If riding, the camel on which he sat would fall to the ground. The Prophet one day, when reclining, with his head on the lap of Zaid, heard the well-known sound: Zaid, too, knew that something unusual was happening, for so heavy became the head of Muhammad that it was with the greatest difficulty he could support the weight. " 

4. At the time of the Mi'raj, or night ascent into heaven, God spoke to the Prophet without the intervention of an angel. It is a disputed point whether the face of the Lord was veiled or not. 

"5. God sometimes appeared in a dream, and placing His hands on the Prophet's shoulders made known His will. 

"6. Twice, angels having each six hundred wings, appeared and brought the message from God. " 

7. Gabriel, though not appearing in bodily form, so inspired the heart of the Prophet, that the words he uttered under its influence were the words of God. This is technically called Ilka (Ilqa'), and is by some supposed to be the degree of inspiration to which the Traditions belong. (See as-Suyutis Itqan, p. 103.) 

"Above all, the Prophet was not allowed to remain in any error; if, by any chance, he had made a wrong deduction from any previous revelation, another was always sent to rectify it. This idea has been worked up to a science of abrogation, according to which some verses of the Qur’an abrogate others. Muhammad found it necessary to shift his stand-point more than once, and thus it became necessary to annul earlier portions of his revelation. 

“Thus in various ways was the revelation made known to Muhammad. At first there seems to have been a season of doubt, the dread lest after all it might be a mockery. But as years rolled on, confidence in himself and in his mission came. At times, too, there is a joyousness in his utterances as he swears by heaven and earth, by God and man; but more often the visions were weird and terrible. Tradition says:" He roared like a camel, the sound as of bells well-nigh rent his heart in pieces." Some strange power moved him, his fear was uncontrollable. For twenty years or more the revelations came, a direction on things of heaven and of earth, to the Prophet as the spiritual guide of all men, to the Warrior-Chief, as the founder of political unity among the Arab tribes."