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  

Yahya related to me from Malik from Yahya ibn Said from Amra bint Abd ar-Rahman that A'isha, the wife of the Prophet ﷺ said, "The Messenger of Allah ﷺ used to pray subh and the women would leave wrapped in their garments and they could not yet be recognised in the darkness."  

إِنْ كَانَ رَسُولُ اللَّهِ ﷺ لَيُصَلِّي الصُّبْحَ فَيَنْصَرِفُ النِّسَاءُ مُتَلَفِّعَاتٍ بِمُرُوطِهِنَّ مَا يُعْرَفْنَ مِنَ الْغَلَسِ  

[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  

The Messenger of Allah ﷺ would say the Fajr prayer after which the women would depart wrapped up their woolen garments, being unrecognizable because of the darkness before dawn. (Using translation from Abū Dāʾūd 423)  

عَنْ عَائِشَةَ زَوْجِ النَّبِيِّ ﷺ أَنَّهَا قَالَتْ إِنْ كَانَ رَسُولُ اللهِ ﷺ لَيُصَلِّي الصُّبْحَ فَيَنْصَرِفُ النِّسَاءُ مُتَلَفِّعَاتٌ بِمُرُوطِهِنَّ مَا يُعْرَفْنَ مِنَ الْغَلَسِ