When one joins the congregational Salaat and has missed one Raka'h, should he read the Tashahhud and other Du'a in the last Raka'h behind the Imaam or should he stay quiet as he will have to replace the missed Raka'h and recite the Tashahhud again?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

The last Tashahhud of every prayer is one of the obligations of the prayer, whether the praying person is praying in congregation or individually, and whether or not he missed some Raka's. When the Imaam sits for the last Tashahhud, the people praying behind him have to recite the Tashahhud even if one has missed one or more Raka's. However, the scholars differed in opinion regarding exalting the mention of the Prophet and other supplications that one says after the Tashahhud, when a person had missed one or more Raka's. Some of them are of the view that he should only recite the Tashahhud and repeat it until the Imaam concludes the prayer; after that, he has to stand up to make up whatever Raka's he had missed. This is the opinion of Imaam Ahmad and the Hanbali School. Nonetheless, the Shaafi'ee School is of the view that the person who is preceded in prayer has to say the supplications and exalt the mention of the Prophet exactly as the Imaam does. Anyway, the matter can be resolved easily if the person who is preceded in prayer recites the Tashahhud and exalts the mention of the Prophet and says other supplications, then that is acceptable, and if he only says the Tashahhud, that is also acceptable.

Allaah knows best.