Reciting a Surah in the Third or Fourth Rakaah of the Fardh salaah

Q: Salaah-340: What is the ruling concerning the person who recites a Surah after Surah Faatiha in the third or fourth Rakaah of the Fardh salaah?

Answer: Mistakenly adding a Surah to the third or fourth Rakaah of the fardh salaah or to both will not invalidate the salaah. It will also not be necessary to perform Sajdah Sahw. And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.2