It was narrated that 'Abdur-Rahman bin Yazeed said:

I was with ‘Abdullah bin Mas'ood in Muzdalifah, and he offered the two prayers, each prayer on its own with an adhan and iqamah, and 'Isha' in between them, And he prayed Fajr when the first light of dawn showed, or when someone might say, dawn has broken, and someone else might say, dawn has not broken. Then he said: The Messenger of Allah (ﷺ) said: “These two prayers are to be shifted from their regular time in this place, and people should not come to Muzdalifah until it is dark, and Fajr prayer should be offered at this time."