كتاب الْمَسَاجِدِ وَمَوَاضِعِ الصَّلاَةِ
5
The Book of Mosques and Places of Prayer
(40)
Chapter: It is recommended to pray Subh early, at the beginning of its time, when it is still dark; and the length of recitation therein
(40)
باب اسْتِحْبَابِ التَّبْكِيرِ بِالصُّبْحِ فِي أَوَّلِ وَقْتِهَا وَهُوَ التَّغْلِيسُ وَبَيَانِ قَدْرِ الْقِرَاءَةِ فِيهَا
Sahih Muslim 645 b

'A'isha, the wife of the Messenger of Allah (ﷺ), reported:

The believing women observed the morning prayer with the Messenger of Allah (ﷺ) wrapped in their mantles. They then went back to their houses and were unrecognisable, because of the Messenger of Allah's (ﷺ) praying in the darkness before dawn.
وَحَدَّثَنِي حَرْمَلَةُ بْنُ يَحْيَى، أَخْبَرَنَا ابْنُ وَهْبٍ، أَخْبَرَنِي يُونُسُ، أَنَّ ابْنَ شِهَابٍ، أَخْبَرَهُ قَالَ أَخْبَرَنِي عُرْوَةُ بْنُ الزُّبَيْرِ، أَنَّ عَائِشَةَ، زَوْجَ النَّبِيِّ صلى الله عليه وسلم قَالَتْ لَقَدْ كَانَ نِسَاءٌ مِنَ الْمُؤْمِنَاتِ يَشْهَدْنَ الْفَجْرَ مَعَ رَسُولِ اللَّهِ صلى الله عليه وسلم مُتَلَفِّعَاتٍ بِمُرُوطِهِنَّ ثُمَّ يَنْقَلِبْنَ إِلَى بُيُوتِهِنَّ وَمَا يُعْرَفْنَ مِنْ تَغْلِيسِ رَسُولِ اللَّهِ صلى الله عليه وسلم بِالصَّلاَةِ ‏.‏
Reference : Sahih Muslim 645 b
In-book reference : Book 5, Hadith 294
USC-MSA web (English) reference : Book 4, Hadith 1346
  (deprecated numbering scheme)