Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: The iqamah for the morning prayer had been called, and I stood up to pray the two rak'ahs before Fajr. The Messenger of Allah (peace and blessings be upon him) took hold of my hand, pulled me and said: "Will you pray Fajr as four rak'ahs?"
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11181