Musannaf Ibn Abi Shayba 3:3958

Ali ibn al-Ja'd narrated to us, he said: Hammad ibn Salamah narrated to us, from Anas ibn Sirin, from Ibn Umar, he said: The Prophet, peace and blessings of Allah be upon him, used to pray the two rak'ahs of Fajr while the Adhan was at his ears.