Salamun 'alaika!
Was the Qur'an revealed gradually or all at once?
The month of Ramadan, in which the Quran was brought down, a guidance for the people, and clarification of the guidance and the criterion. Therefore, those of you who witness the month shall fast it. And those who are ill or travelling, then an equal number of other days. God wants ease for you, and He does not want hardship for you, and so that you may complete the count, and to exalt God for guiding you, and that you may be thankful. (2:185)
Those who deny/conceal the truth, say: “Why was the Qur’an not sent down to him all at once?” This is how We sent it in stages, in order to strengthen your heart with it and We read it slowly, in stages. (25:32)
Wasalaam!