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

Bukhari :: Book 3 :: Volume 33 :: Hadith 246

Narrated 'Aisha:

(the wife of the Prophet) Allah's Apostle used to let his head in (the house) while he was in the mosque and I would comb and oil his hair. When in Itikaf he used not to enter the house except for a need.