Performing the prayer in congregation in the mosque is of great significance and subject to particular rulings. When the congregational prayer commences, no one should embark upon another prayer. Rather, the Muslim should join the prayer whose iqāmah has been proclaimed. This is the command and guidance of the Prophet (may Allah's peace and blessings be upon him). In this Hadīth, ‘Abdullāh ibn Sarjis (may Allah be pleased with him) relates that a man entered the mosque while the Messenger of Allah (may Allah's peace and blessings be upon him) was leading his Companions in "the Morning prayer", which is the Fajr prayer. Before joining the congregational prayer with the Prophet (may Allah's peace and blessings be upon him), he offered two Rak‘ahs as the Sunnah of the Fajr prayer alone in a corner of the mosque. Then, he entered the congregational prayer along with the Prophet (may Allah's peace and blessings be upon him). After the Prophet (may Allah's peace and blessings be upon him) finished the prayer, he called him - O so and so - and asked him: Which one of the two prayers have you counted as your obligatory prayer, "your prayer alone or your prayer with us?!" Which one have you counted as the obligatory prayer and which one the supererogatory prayer?! These are words of reprimand and rebuke from the Prophet (may Allah's peace and blessings be upon him) for his performance of the supererogatory prayer while the Imām was offering the obligatory prayer. But this does not indicate that any of the two prayers is invalid. In the Hadth: Evidence that after the iqmah is proclaimed, one should not embark upon a supererogatory prayer, even if he will be able to join the prayer with the Imam..