Sahih Bukhari
Sahih Bukhari Volume 003, Book 033, Hadith Number 243.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 33. Retiring To a Masjid for Remembrance Of Allah (I'tikaf)
Narated By 'Aisha : (The wife of the Prophet) The Prophet used to practice Itikaf in the last ten days of Ramadan till he died and then his wives used to practice Itikaf after him.