Does a worshipper's seeing Satan in front of him during prostration, accompanied by a feeling that he is worshipping Satan, invalidate his prayer and necessitate its repetition, and what should he do about that?

The best way to expel Satan and his whispers during prayer is to seek refuge in Allah from the accursed Satan and to spit to one's left three times, based on the hadith (definition) of Uthman ibn Abi al-Aas with the Prophet, peace be upon him, concerning a devil named Khanzab. It should be noted that excessive movement in prayer that is not part of the prayer itself invalidates it. The questioner is advised to seek out a ruqya practitioner who uses the Quran and Sunnah (definition), as there is a possibility that he may be afflicted by jinn possession.