Musannaf Ibn Abi Shayba 3:4824

Abu Bakr narrated to us, he said: Isma'il ibn 'Ulayyah narrated to us, from Ayyub, from Ibn Sirin, who said: I was informed that Abu Musa al-Ash'ari repeated the morning prayer three times in one day. He prayed, then sat, then it became clear to him that he had prayed during the night, so he repeated it. Then he prayed and sat until it became clear that he had prayed during the night, so he repeated it a third time.