Bulugh al-Maram 2 The Book of Prayer كتاب الصلاة 6

وَلِمُسْلِمٍ مِنْ حَدِيثِ أَبِي مُوسَى: { فَأَقَامَ اَلْفَجْرَ حِينَ اِنْشَقَّ اَلْفَجْرُ, وَالنَّاسُ لَا يَكَادُ يَعْرِفُ بَعْضُهُمْ بَعْضًا }

Narrated Abu Musa (RA) in another version of Muslim: He (صلى الله عليه وسلم) offered the Fajr prayer at daybreak when the people could hardly recognize one another.