Offering obligatory Prayer behind an Imam offering a Nafilah Prayer

A: What you have done is permissible for it is generally allowed for whoever prays obligatory Salah to pray as a Ma'mum behind someone who is praying a Nafilah (supererogatory) one. Proof for the foregoing is that Mu`adh (may Allah be pleased with him) would pray firstly as a Ma'mum behind the Prophet (peace be upon him) then he would pray the same obligatory Salah as an Imam for his people which would count for him as a Nafilah Prayer. On the other hand, the fact that the man you prayed behind did not recite in Jahr does not change the ruling mentioned above as reciting in Jahr is Sunnah (a commendable act) in Fajr and all Salahs (Prayers) which are performed at night.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.