The second revelation of the Holy Quran, which was gradual, began when the age of the Holy Prophet (peace be upon him) was forty years.
The following information is proven from the Holy Quran itself regarding this revelation of the Holy Quran.
(1) The beginning of this revelation took place in the month of Ramadan.
(2) The night on which this revelation began was Laylat al-Qadr.
(3) This was the same date on which the Battle of Badr later took place.
Reference: Tuhfa Hufaz;