Reciting a Surah before the Surah Faatiha

Q: Salaah-507: If a person recited a Surah before the Surah Faatiha and then realised his error, what is he supposed to do? Should he leave the Surah to recite the Surah Faatiha or first complete the Surah and then recite Surah Faatiha? Will Sajdah Sahw be necessary?

Answer: He ought to leave the Surah. recite Surah Faatiha and then recite a Surah again. If a verse of the Surah was recited before the Surah Faatiha, Sajdah Sahw will be necessary because a verse is the absolute minimum Qiraa'ah required and it will be a cause for delaying the recitation of Surah Faatiha. However, if he recited less than a verse, Sajdah Sahw will not be necessary. And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.2