It is narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that once the Prophet (peace and blessings of Allah be upon him) led us in the prayer of fear (Salat al-Khawf). The noble Companions (may Allah be pleased with them) stood in two rows: one row behind the Prophet (peace be upon him) and the other row facing the enemy. The Prophet (peace be upon him) led those standing behind him in one rak'ah, then these people stood up and went to stand in front of the enemy, and those in the second row came and stood in the place of the first row. The Prophet (peace be upon him) also led them in one rak'ah and then said salam. Then these people stood up and themselves prayed one rak'ah and after saying salam, went to stand in front of the enemy in the place of the first row, and the people of the first row returned to their place and prayed one rak'ah and then said salam.