Musannaf Ibn Abi Shaybah 8515 — The fear prayer: how many rakahs it is

Sayyiduna Sahl bin Abi Hathmah (may Allah be pleased with him) said about the fear prayer: The imam will stand facing the qiblah, and one group will pray with him while the other group stands facing the enemy. He will lead this group in one rak'ah. When he stands for the second rak'ah, he should remain standing until the group behind him prays its one rak'ah on its own, prostrates and gives the salam. Then these people will go towards the enemy, and the group that was already facing the enemy should come and stand behind the imam; the imam should lead them in one rak'ah and give the salam. Then those behind him should bow on their own, prostrate and give the salam.