We were commanded to go out as well as the hidden away ladies and those unmarried. She said menstruating women were to come out amongst you, but remain behind people and pronounce takbir (Allah-o-Akbar) along with them. (Using translation from Muslim 890b)
«كُنَّا نُؤْمَرُ بِالْخُرُوجِ فِي الْعِيدَيْنِ وَالْمُحَيَّاةُ وَالْبِكْرُ قَالَتْ وَالْحُيَّضُ يَخْرُجْنَ فَيَكُنَّ خَلْفَ النَّاسِ يُكَبِّرْنَ مَعَ النَّاسِ»