Sunan Ibn Majah · Book 2 · Hadith 669
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنِ الزُّهْرِيِّ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ، قَالَتْ كُنَّ نِسَاءُ الْمُؤْمِنَاتِ يُصَلِّينَ مَعَ النَّبِيِّ ـ صلى الله عليه وسلم ـ صَلاَةَ الصُّبْحِ ثُمَّ يَرْجِعْنَ إِلَى أَهْلِهِنَّ فَلاَ يَعْرِفُهُنَّ أَحَدٌ . تَعْنِي مِنَ الْغَلَسِ .
It was narrated that 'Aishah said: "The believing women used to perform the Subh prayer with the Prophet, then they would go back to their families and no one would recognize them," meaning of the darkness.
Sahih