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

Bukhari :: Book 3 :: Volume 33 :: Hadith 250

Narrated 'Aisha:

The Prophet intended to practice Itikaf and when he reached the place where he intended to perform Itikaf, he saw some tents, the tents of 'Aisha, Hafsa and Zainab. So, he said, "Do you consider that they intended to do righteousness by doing this?" And then he went away and did not perform Itikaf (in Ramadan) but performed it in the month of Shawwal for ten days.