Al-Qasim bin Hassan (may Allah have mercy on him) narrates: I asked Sayyiduna Zayd bin Thabit (may Allah be pleased with him) about the prayer of fear, and he said: "The Messenger of Allah (peace and blessings be upon him) stood and led them in prayer. One row stood behind him (peace and blessings be upon him) and one row remained standing facing the enemy. He (peace and blessings be upon him) led them in one rak'ah; then these people went to the place of the other row, and those people came, and he (peace and blessings be upon him) led them too in one rak'ah; then he concluded the prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4900