Musnad Ahmad 26:419

Yahya ibn Adam narrated to us, Isra'il narrated to us, from Abu Ishaq, from 'Abd al-Rahman ibn Yazid, who said: I was with 'Abdullah ibn Mas'ud at Jam' (Muzdalifah), and he performed the two prayers, each prayer separately with an Adhan and an Iqamah, and the dinner (supper) was between them. He performed the Fajr prayer when the dawn broke, or he said: When a person said, "The dawn has broken," and another person said, "It has not broken." Then he said: The Messenger of Allah (ﷺ) said: "These two prayers are shifted from their times in this place. People do not arrive at Jam' until they are in the darkness of the night, and the Fajr prayer is at this hour."