What should you do if you experience inappropriate thoughts and words during prayer; do you complete the prayer or repeat it?

One must ward off the whispers of Satan and seek refuge in Allah from him, and preoccupy oneself with contemplating the remembrances (dhikr), the Quran, and supplications (du'a). The one afflicted by whispers should associate with righteous people and participate with them in good deeds, and frequently read books that encourage virtuous acts of worship. Forgetfulness during the recitation of Surah Al-Fatihah does not invalidate the prayer, but completely abandoning its recitation does invalidate it.