Quran is the word of God that was revealed in Arabic to prophet Muhammad who is the last prophet as stated clearly in the Quran in 33:40. This makes Quran the final testament to mankind. It was placed into Muhammad's soul on the 27th night of Ramadan, 13 B.H. (Before Hijrah) through the mediation of Angel Gabriel and witnessed by the angels (4:166):
[2:97] Say, "Anyone who opposes Gabriel should know that he has brought down this (Quran) into your heart, in accordance with GOD's will, confirming previous scriptures, and providing guidance and good news for the believers."
[97:1] We revealed it in the Night of Destiny.
[97:2] How awesome is the Night of Destiny!
[97:3] The Night of Destiny is better than a thousand months.
[97:4] The angels and the Spirit descend therein, by their Lord's leave, to carry out every command.
[97:5] Peaceful it is until the advent of the dawn.
[16:2] He sends down the angels with the revelations, carrying His commands, to whomever He chooses from among His servants: "You shall preach that there is no other god beside Me; You shall reverence Me.
[53:1] As the stars fell away.
[53:2] Your friend (Muhammad) was not astray, nor was he deceived.
[53:3] Nor was he speaking out of a personal desire.
[53:4] It was divine inspiration.
[53:5] Dictated by the Most Powerful.
[53:6] Possessor of all authority. From His highest height.
[53:7] At the highest horizon.
[53:8] He drew nearer by moving down.
[53:9] Until He became as close as possible.
[53:10] He then revealed to His servant what was to be revealed.
Subsequently, Gabriel helped Muhammad release few verses of the Quran at a time, from his soul to his memory:
[17:106] A Quran that we have released slowly, in order for you to read it to the people over a long period, although we sent it down all at once.