Musannaf Ibn Abi Shayba 35:399

Ya'la narrated to us, from al-Ajalih, from 'Ata', who said: I saw Ibn Umar and Ibn al-Zubayr perform Tawaf around the House before the dawn prayer, then they prayed two rak'ahs before the rising of the sun. And he mentioned that Abu Hanifah said: He prays when it sets or rises, and prayer is permitted.