Nafi' (may Allah have mercy on him) narrates from Ibn Umar (may Allah be pleased with them both) that Ibn Umar (may Allah be pleased with them both) would not pray in the early part of the day until the sun had passed its zenith. One day he prayed, and that was after the sun had risen, so he said: I had not prayed the two rak'ahs of Fajr.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4559