Sahih Bukhari Volume 2, Book 13, Hadith 982

حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، قَالَ حَدَّثَنَا ابْنُ أَبِي عَدِيٍّ، عَنِ ابْنِ عَوْنٍ، عَنْ مُحَمَّدٍ، قَالَ قَالَتْ أُمُّ عَطِيَّةَ أُمِرْنَا أَنْ نَخْرُجَ فَنُخْرِجَ الْحُيَّضَ وَالْعَوَاتِقَ وَذَوَاتِ الْخُدُورِ‏.‏ قَالَ ابْنُ عَوْنٍ أَوِ الْعَوَاتِقَ ذَوَاتِ الْخُدُورِ، فَأَمَّا الْحُيَّضُ فَيَشْهَدْنَ جَمَاعَةَ الْمُسْلِمِينَ وَدَعْوَتَهُمْ، وَيَعْتَزِلْنَ مُصَلاَّهُمْ‏

Narrated By Um-'Atiya : We were ordered to go out (for 'Id) and also to take along with us the menstruating women, mature girls and virgins staying in seclusion. (Ibn 'Aun said, "Or mature virgins staying in seclusion)." The menstruating women could present themselves at the religious gathering and invocation of Muslims but should keep away from their Musalla.