"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.  

كُنَّ نِسَاءُ الْمُؤْمِنَاتِ يُصَلِّينَ مَعَ النَّبِيِّ ﷺ صَلاَةَ الصُّبْحِ ثُمَّ يَرْجِعْنَ إِلَى أَهْلِهِنَّ فَلاَ يَعْرِفُهُنَّ أَحَدٌ تَعْنِي مِنَ الْغَلَسِ  

The Messenger of Allah recited: And recite the Qur'an during the Fajr. Verily, the recitation of the Qur'an during Fajr is ever witnessed." He said: "It is witnessed by the angels of the night and the day."  

عَنْ رَسُولِ اللَّهِ ﷺ {وَقُرْآنَ الْفَجْرِ إِنَّ قُرْآنَ الْفَجْرِ كَانَ مَشْهُودًا} قَالَ تَشْهَدُهُ مَلاَئِكَةُ اللَّيْلِ وَالنَّهَارِ  

"I prayed the Subh with 'Abdullah bin Zubair in the darkness, and when he said the Taslim, I turned to Ibn 'Umar and said: 'What is this prayer?' He said: 'This is how we prayed with the Messenger of Allah and with Abu Bakr and 'Umar. When 'Umar was stabbed, 'Uthman delayed it until there was light.'"  

هَذِهِ صَلاَتُنَا كَانَتْ مَعَ رَسُولِ اللَّهِ ﷺ وَأَبِي بَكْرٍ وَعُمَرَ فَلَمَّا طُعِنَ عُمَرُ أَسْفَرَ بِهَا عُثْمَانُ  

The Prophet said: "Pray the Subh early, for indeed its reward is greater" or "your reward."  

أَنَّ النَّبِيَّ ﷺ قَالَ أَصْبِحُوا بِالصُّبْحِ فَإِنَّهُ أَعْظَمُ لِلأَجْرِ أَوْ لأَجْرِكُمْ