Musnad Abu Ya'la al-Mawsili 152:285

Abu Khaythama narrated to us, Muhammad ibn Fudayl narrated to us, from Khusayf, Abu Ubayda narrated to us, from Abdullah, who said: The Messenger of Allah (may Allah bless him and grant him peace) led us in the prayer of fear. They stood in two rows: a row stood behind the Prophet (may Allah bless him and grant him peace), and a row stood facing the enemy. The Messenger of Allah (may Allah bless him and grant him peace) prayed one rak'ah with the row that was next to him. Then they stood up and went and stood in the place of those who were facing the enemy, and those [others] came and stood in their place. The Messenger of Allah (may Allah bless him and grant him peace) prayed with them, then he performed the taslim. Then they stood up and prayed one rak'ah for themselves, then they performed the taslim. Then they went and stood in the place of those who were facing the enemy, and those [others] returned to their place and prayed one rak'ah for themselves, then they performed the taslim.