If Surah Faatiha is Repeated?

Q: Salaah-32: Will Sajdah Sahw be necessary if Surah Faatiha is erroneously repeated in salaah?

Answer: Sajdah Sahw will be Waajib (compulsory) if Surah Faatiha is repeated in error because this amounts to delaying the recitation of another Surah to link with the Surah Faatiha. Sajdah Sahw will however not be necessary if it is repeated after reciting the Surah. Saldah Sahw will also not be necessary if Surah Faatiha is repeated in the last two Rakaahs of a Fardh obligatory) salaah. And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.2