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 and blessings of Allah be upon him), and the other row facing the enemy. Altogether, they were all engaged in prayer. The Prophet (peace and blessings of Allah be upon him) said the takbir, and all the people said the takbir with him. Then the Prophet (peace and blessings of Allah be upon him) led those standing in the row behind him in one rak'ah. Then these people stood up and went to stand in front of the enemy in place of the others, and the second row came and stood in the place of the first row. The Prophet (peace and blessings of Allah be upon him) also led them in one rak'ah and then said the salam. Then these people stood up and themselves prayed one rak'ah and, after saying the salam, went to stand in front of the enemy in place of the first row, and the first row returned to their place and prayed one rak'ah.