Sahih Bukhari Volume 001, Book 008, Hadith Number 347.
Narated By Um 'Atiya : We were ordered to bring out our menstruating women and veiled women in the religious gatherings and invocation of Muslims on the two 'Id festivals. These menstruating women were to keep away from their Musalla. A woman asked, "O Allah's Apostle ' What about one who does not have a veil?" He said, "Let her share the veil of her companion."