Musannaf Ibn Abi Shaybah 8508 — The fear prayer: how many rakahs it is

Al-Hasan was asked about the fear prayer, and he said: I was told from Sayyiduna Jabir bin Abdullah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) led his Companions in the fear prayer in this way: he led one group in prayer while one group stood facing the enemy. He led the group behind him in two rak'ahs; then this group went off towards the enemy, and the other group came and prayed two rak'ahs behind him. Then he gave the salam.