Musnad Ahmad 26:90

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from 'Umarah, from 'Abd al-Rahman ibn Yazid, who said: 'Abdullah said: "I did not see the Messenger of Allah, may Allah bless him and grant him peace, perform any prayer except at its appointed time, except for two prayers: the Maghrib and Isha prayers at Jam' (Muzdalifah), and the Fajr prayer on that day, before its [usual] appointed time."