If Masbooq misses the tashahud whilst completing Maghrib salah

In the name of Allah, the most Beneficent, the most Merciful.

Answer

If a person finds one rakaat of the Maghrib Salah with the Imam and misses two rakaats then the masbooq should complete the remaining two rakaats by performing qaidah and tashahud in between.  If someone omits it then sajdah sahwe will be necessary.   (Fatawa Darul Uloom Deoband p.397 v.3)

Only Allah Knows Best

Mohammed Tosir Miah

Darul Ifta Birmingham.