Sahih Bukhari Volume 003, Book 032, Hadith Number 233.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 32. Praying at Night In Ramadhan (Taraweeh)
Narated By Abu Salama : I asked Abu Sa'id, and he was a friend of mine, (about the Night of Qadr) and he said, "We practiced Itikaf (seclusion in the mosque) in the middle third of the month of Ramadan with the Prophet. In the morning of the 20th of Ramadan, the Prophet came and addressed us and said, 'I was informed of (the date of the Night of Qadr) but I was caused to forget it; so search for it in the odd nights of the last ten nights of the month of Ramadan. (In the dream) I saw myself prostrating in mud and water (as a sign). So, whoever was in l'tikaf with me should return to it with me (for another 10-day's period)', and we returned. At that time there was no sign of clouds in the sky but suddenly a cloud came and it rained till rain-water started leaking through the roof of the mosque which was made of date-palm leaf stalks. Then the prayer was established and I saw Allah's Apostle prostrating in mud and water and I saw the traces of mud on his forehead."