Retiring to a Mosque for Remembrance of Allah (I'tikaf)

Bukhari :: Book 3 :: Volume 33 :: Hadith 252

Narrated Abu Salama bin 'Abdur-Rahman:

I asked Abu Said Al-Khudri, "Did you hear Allah's Apostle talking about the Night of Qadr?" He replied in the affirmative and said, "Once we were in Itikaf with Allah's Apostle in the middle ten days of (Ramadan) and we came out of it in the morning of the twentieth, and Allah's Apostle- delivered a sermon on the 20th (of Ramadan) and said, 'I was informed (of the date) of the Night of Qadr (in my dream) but had forgotten it. So, look for it in the odd nights of the last ten nights of the month of Ramadan. I saw myself prostrating in mud and water on that night (as a sign of the Night of Qadr). So, whoever had been in Itikaf with Allah's Apostle should return for it.' The people returned to the mosque (for Itikaf). There was no trace of clouds in the sky. But all of a sudden a cloud came and it rained. Then the prayer was established (they stood for the prayer) and Allah's Apostle prostrated in mud and water and I saw mud over the forehead and the nose of the Prophet.