مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4110
Musnad of Abdullah bin Mas'ood
It was narrated that ‘Abdullah (رضي الله عنه) said: I never saw the Messenger of Allah (ﷺ) offer any prayer but it was on time, except that he put together 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).
Musnad Ahmad 4137Its isnad is saheeh, al-Bukhari (1682) and Muslim (1289)]