Answer:
(Fatwa: 322/322/M=1431)
Supplicating after fardh salah is proved from Hadith; therefore the imam is not wrong to do so. There is nothing wrong if it takes the form of collectivity, but after salam, the salah comes to an end, one can go if he has any need without participating.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband
