It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both), who narrates from Hafsah (may Allah be pleased with her), that the Prophet (peace and blessings be upon him) used to pray two light rak'ahs after the dawn had broken and the caller had called the adhan for the prayer.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19622