Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates from Hafsah (may Allah be pleased with her) that when the mu'adhdhin called the adhan for Fajr, the Messenger of Allah (peace and blessings be upon him) would stand and pray the two rak'ahs of Fajr, then go out to the mosque, and he would make food forbidden (upon himself); and the adhan was not called until it was morning.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19625