Al-Matalib al-'Aliyah 742 — The fear prayer

It is narrated from Abu al-Aliyah al-Riyahi (may Allah have mercy on him) that Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him) was staying in a house (or district) of Isfahan, and in those days there was no particular fear or danger from the enemy there; but he wished to teach the people their religion and the Sunnah of their Prophet (peace and blessings be upon him). So he formed the people into two groups: one group, armed, stood in rows facing the enemy, and the other group stood behind him for the prayer. He (may Allah be pleased with him) led the group next to him in one rak'ah; then they stepped back on their heels until they reached the place of the other group, passing through one another to change places, until they (the others) came and stood behind the imam. Then he (may Allah be pleased with him) led them in another rak'ah and gave the salam. After that all the people of the first group and the second group stood and performed their remaining one rak'ah each individually, and then gave the salam. In this way the imam's two rak'ahs were completed in congregation, and the followers also completed one rak'ah each behind the imam.
Its narrators are thiqat (trustworthy), but there is a break (inqita') in its chain between Abu al-Aliyah and Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him).