Hisnul Muslim 138

For one afflicted by whisperings in prayer or recitation

أَعُوذُ بِاللَّهِ مِنَ الشَّيْطَانِ الرَّجيمِ

'A 'oothu billaahi minash-Shaytaanir-rajeem.

I seek refuge in Allah from Satan the outcast. Then spit to your left three times.