Sayyiduna Ibn Abbas (may Allah be pleased with them both) was asked about the verse: "The month of Ramadan in which the Qur'an was sent down" [Surah al-Baqarah: 185] and the verse: "Indeed, We sent it down on a blessed night" [Surah al-Dukhan: 3]. He said: "It was sent down in Ramadan, on the Night of Decree (Laylat al-Qadr), on a blessed night, all at once; then it was sent down little by little over the months and days."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12043