Sayyiduna Abdullah (may Allah be pleased with him) said: I never saw the Prophet (peace and blessings be upon him) pray any prayer outside its time except two prayers: he combined Maghrib and Isha at Muzdalifah, and he prayed the Fajr prayer before its appointed time.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 9518