Sayyiduna Ibn Umar (may Allah be pleased with them both) said: "The Messenger of Allah (peace and blessings be upon him) led the fear prayer (salat al-khawf): he led one of the two groups in one rak'ah while the other group stayed facing the enemy. Then they turned away and stood in the place of their companions, facing the enemy, and the (other) group came, and the Prophet (peace and blessings be upon him) led them in one rak'ah. Then he (peace and blessings be upon him) gave the salam, then these completed their one rak'ah and those completed their one rak'ah."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13058