Amr bin Dinar narrates: I saw Ibn Umar (may Allah be pleased with them both) perform tawaf after the Fajr prayer, then he prayed two rak'ahs, then he said: It is only disliked at the time the sun is rising, because the Messenger of Allah (peace and blessings be upon him) said: "The sun rises between the two horns of Satan."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13591