Sahih Muslim
Sahih Muslim 1289 a
It is recommended to pray Subh when it is still dark on the day of sacrifice in Al-Muzdalifah, and to do it very early after ascertaining that dawn has broken
Arabic hadith text
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، وَأَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ وَأَبُو كُرَيْبٍ جَمِيعًا عَنْ أَبِي مُعَاوِيَةَ، - قَالَ يَحْيَى أَخْبَرَنَا أَبُو مُعَاوِيَةَ، - عَنِ الأَعْمَشِ، عَنْ عُمَارَةَ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ يَزِيدَ، عَنْ عَبْدِ اللَّهِ، قَالَمَا رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم صَلَّى صَلاَةً إِلاَّ لِمِيقَاتِهَا إِلاَّ صَلاَتَيْنِ صَلاَةَ الْمَغْرِبِ وَالْعِشَاءِ بِجَمْعٍ وَصَلَّى الْفَجْرَ يَوْمَئِذٍ قَبْلَ مِيقَاتِهَا .
Translation
A'bdullah (b. 'Umar) reported
I have never seen Allah's Messenger, (ﷺ) but observing the prayers at their appointed times except two prayers, sunset and 'Isha, ' at Muzdalifa (where he deferred the sunset prayer to combine it with 'Isha' and he observed the dawn prayer before its stipulated time on that day (10th of Dhu'l-Hijja).