It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) used to recite Surah al-Kafirun and Surah al-Ikhlas in the two rak'ahs of Fajr.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13067