Musannaf Ibn Abi Shaybah 8496 — The fear prayer: how many rakahs it is

Abu al-Aliyah said: Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him) was in an area of Isfahan. They did not have much fear of the enemy, but he wanted to teach the people their religion and the Sunnah of the Prophet (peace and blessings be upon him). So he formed the people into two groups: one group he stood facing the enemy with weapons, and the other group he kept behind him. He led the group behind him in one rak'ah; then they walked backwards to the place of the other group, facing the enemy. Then that group came and stood behind Sayyiduna Abu Musa, and he led this group in the second rak'ah. Then he gave the salam. Then the people who had prayed the first rak'ah and gone to face the enemy came and prayed one rak'ah, and the others also prayed one rak'ah. Then they gave the salam to one another. In this way the imam completed two rak'ahs, and each of the two groups had one rak'ah behind the imam.