Sahih Bukhari Volume 003, Book 033, Hadith Number 248.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 33. Retiring To a Masjid for Remembrance Of Allah (I'tikaf)
Narated By Ibn 'Umar : Umar asked the Prophet "I vowed in the Pre-lslamic period of ignorance to stay in Itikaf for one night in Al-Masjid al-Haram." The Prophet said to him, "Fulfill your vow."