Musannaf Ibn Abi Shayba 3:5897

Muhammad ibn Bishr narrated to us, he said: Sa’id narrated to us, from Qatadah, from Abu al-Aliyah al-Riyahi, that Abu Musa al-Ash’ari was in the house [garrison] of Isfahan, and there was not much fear among them at that time, but he liked to teach them their religion and the Sunnah of their Prophet, may Allah bless him and grant him peace. So he arranged them into two rows: a group with their weapons facing their enemy, and a group behind them. He prayed one rak'ah with those who were with him, then they retreated on their heels until they stood in the place of the others, passing through them until they stood behind him. Then he prayed another rak'ah with them and performed the taslim. Then those who were next to him and the others stood up and prayed one rak'ah each, and they performed the taslim to one another. Thus, two rak'ahs were completed for the Imam in congregation, and one rak'ah each for the people.