Messenger of Allah ﷺ used to offer the Fajr prayer when it was still dark and the believing women used to return (after finishing their prayer) and nobody could recognize them owing to darkness, or they could not recognize one another.
أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ يُصَلِّي الصُّبْحَ بِغَلَسٍ فَيَنْصَرِفْنَ نِسَاءُ الْمُؤْمِنِينَ لاَ يُعْرَفْنَ مِنَ الْغَلَسِ أَوْ لاَ يَعْرِفُ بَعْضُهُنَّ بَعْضًا
[Machine] The Prophet ﷺ used to pray Fajr (morning prayer) and then the believing women would leave wrapped in their outer garments, concealing themselves with what is known as a "ghalas" or, some of them do not recognize others.
كَانَ رَسُولُ اللهِ ﷺ يُصَلِّي الصُّبْحَ فَيَنْصَرِفُ نِسَاءُ الْمُؤْمِنِينَ مُتَلَفِّعَاتٍ بِمُرُوطِهِنَّ مَا يُعْرَفْنَ مِنَ الْغَلَسِ أَوْ قَالَ لَا يَعْرِفُ بَعْضُهُنَّ بَعْضًا
"عَنْ عَائِشَةَ قَالَتْ: كَانَ رَسُولُ اللهِ ﷺ يُصَلِّي الصُّبْحَ وَتَنْصَرِفُ النِّسَاءُ المْؤُمِنَاتُ مُتَلَفِّعَاتٍ بِمُرُوطِهِنَّ لَا يُعْرَفْنَ، وَلَا يَعْرِفُ بَعْضُهُنَّ بَعْضًا مِنَ الغَلَسِ".