Abu Dawud Book 2, Hadith Number 1377.

Chapter : The view that the twentyfirst night of ramadhan is lailat alqadr.

Narated By Abu Sa’id al-Khudri : The Apostle of Allah (PBUH) used to spend the middle ten days of Ramadhan in retirement and devotion (i’tikaf) in the mosque. One year he had retirement and devotion in the mosque (as usual); when the twenty-first night came, and this is the night when he used to come out of his devotion in the mosque, he said: He who engaged himself in devotion along with me should do so during the last ten days; I saw that night, then was caused to forget it, but I have seen myself prostrating in water and mud on the morning following (that night), so seek it in the last ten days and seek it in every night with an odd number. Abu Sa’id said: Rain fell that night, the mosque that was a thatched building dripped, and my eyes saw the Apostle of Allah (PBUH) with traces of water and mud, on his forehead on the morning following the twenty-first night.