Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates from Hafsah (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) prayed the two rak'ahs of Fajr as soon as the dawn broke.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19685