كتاب الصلاة
2  
The Book of Prayer
Narrated Abu Musa (RA) in another version of Muslim:
He (ﷺ) offered the Fajr prayer at daybreak when the people could hardly recognize one another.
وَلِمُسْلِمٍ مِنْ حَدِيثِ أَبِي مُوسَى: { فَأَقَامَ اَلْفَجْرَ حِينَ اِنْشَقَّ اَلْفَجْرُ, وَالنَّاسُ لَا يَكَادُ يَعْرِفُ بَعْضُهُمْ بَعْضًا }

Sunnah.com reference : Book 2, Hadith 6
Arabic/English book reference : Book 2, Hadith 156