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

Bukhari :: Book 3 :: Volume 33 :: Hadith 253

Narrated 'Aisha:

One of the wives of Allah's Apostle practiced Itikaf with him while she ad bleeding in between her periods and she would see red (blood) or yellowish traces, and sometimes we put a tray beneath her when she offered the prayer.