Nafi' narrates from Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) led the fear prayer: one group stood with him (peace and blessings be upon him) and the other group faced the enemy. He (peace and blessings be upon him) led them in one rak'ah. Then these went to the others' place and those came to their place. Then he (peace and blessings be upon him) led them in one rak'ah. Then he (peace and blessings be upon him) gave the salam. Then both groups each completed their own one rak'ah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الخوف / 6041