Musnad Ahmad 4020

It was narrated that 'Abdullah said: I never saw the Messenger of Allah (ﷺ) offer any prayer but it was on time, except two prayers; Maghrib and 'Isha' in Muzdalifah, and he prayed Fajr on that day before the time when he usually prayed it (but after ascertaining that dawn had broken). And Ibn Numair said: (Maghrib and 'Isha'), and he prayed them together in Muzdalifah.