Someone has performed the obligatory Prayer and leads a congregation who have not yet performed the obligatory Prayer

A: It is permissible for anyone who performed the obligatory prayer to lead a congregation who have not yet performed the obligatory prayer. In this case, the Salah will be Nafilah (supererogatory) for the Imam and obligatory for the congregation. It is reported by Muslim in his Sahih on the authority of Jabir ibn `Abdullah that Mu`adh used to offer Salah with the Prophet (peace be upon him) and then return to his people to lead their congregation in the same Salah. Furthermore, Abu Dawud and others narrated that when the Prophet (peace be upon him) saw a man who missed the congregational Prayer, he said, Is there any man who may do good with this (man) and pray along with him? Accordingly, it is permissible for a person who offers Nafilah to pray behind an Imam who offers the obligatory Salah and vice versa. Therefore, you are not required to repeat the Salah you performed behind this Imam. Likewise, the group that joined your congregation are not required to repeat it.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.