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, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
The Sunnah of the Naafilah is that the one praying recites Al-Faatihah and something else that is easy for him of other Soorahs. However, if he limited himself to Al-Faaithah alone, then his prayer is still valid, even if that is not in accordance with the Sunnah.