Musannaf Ibn Abi Shayba 3:5913

'Abd al-A'la narrated to us, from Yunus, from al-Hasan, that Abu Musa prayed with his companions in Isfahan. A group of them prayed with him, and a group faced the enemy. He prayed one rak'ah with them, then they retreated, and the others came, passing through them. He prayed one rak'ah with them, then he performed the taslim. Then the two groups stood up and prayed one rak'ah.