Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates, through Hafsah (may Allah be pleased with her), from the Messenger of Allah (peace and blessings be upon him) that when the adhan was called for the Fajr prayer, he (peace and blessings be upon him) would pray two light rak'ahs before standing for the prayer.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19624