Supplication for one afflicted with doubt in his faith:
He should seek refuge in Allah. He should renounce that which is causing such doubt.
He should say:
آمَنْتُ بِاللهِ وَرُسُلِهِ
‘I have believed in Allaah and His Messengers.’
هُوَ الأَوَّلُ وَالآخِرُ وَالظَّاهِرُ وَالبَاطِنُ وَهُوَ بِكُلِّ شَيءٍ عَلِيْمٌ
‘He is The First and The Last, ath-Thaahir and al-Baatin and He knows well all things.’ [al-Hadeed, Aayah 3]