Musnad Abu Ya'la al-Mawsili 152:196

Muhammad ibn Abi Bakr narrated to us, Ibn Mahdi narrated to us, from Sufyan, from al-A’mash, from ‘Umarah, from ‘Abd al-Rahman ibn Yazid, from ‘Abdullah, who said: I did not see the Messenger of Allah (may Allah bless him and grant him peace) pray any prayer except at its time, for its appointed time, except that he combined the Maghrib and the ‘Isha’ at Jam’ (Muzdalifah), and he prayed the Subh (Fajr) prayer before its (usual) time.