It is narrated from Hazrat Yazid bin Aswad (may Allah be pleased with him) that I participated in the Farewell Pilgrimage with the Prophet (peace and blessings of Allah be upon him). I offered the Fajr prayer with the Prophet (peace and blessings of Allah be upon him) in the Mosque of Khaif. When the Prophet (peace and blessings of Allah be upon him) finished the prayer, he saw that at the end of the mosque two men were sitting and had not participated in the prayer with him. The Prophet (peace and blessings of Allah be upon him) said, "Bring both of them to me." When they were brought, they were trembling with fear. The Prophet (peace and blessings of Allah be upon him) asked, "Why did you not pray with us?" They replied, "O Messenger of Allah (peace and blessings of Allah be upon him), we had already prayed in our tents." The Prophet (peace and blessings of Allah be upon him) said, "Do not do so. If you have already prayed in your tents and then you come to the mosque at the time of congregation, then join in the prayer, for this will be a voluntary prayer for you."