Allah, exalted be His praise, says: "In the name of Allah, the Most Gracious, the Most Merciful."
"Indeed, We sent it (the Qur'an) down on the Night of Decree. And what will make you know what the Night of Decree is? The Night of Decree is better than a thousand months. The angels and the Spirit (Jibril) descend therein by the permission of their Lord for every matter. Peace it is, until the rising of the dawn." [Surah al-Qadr: 1-5]
Sa'id bin Jubayr (may Allah have mercy on him) narrates from Sayyiduna Ibn Abbas (may Allah be pleased with them both) regarding the saying of Allah Almighty, "Indeed, We sent it down on the Night of Decree" [Surah al-Qadr: 1], that the Qur'an was sent down all at once to the lowest heaven on the Night of Decree, and it was at the place where the stars descend, and Allah Almighty would send it down as occasions required, one revelation after another. Allah Almighty says: They said, "Why was the Qur'an not sent down to him all at once?" [Surah al-Furqan: 32] "So that We may strengthen your heart thereby." [Surah al-Furqan: 32]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8521