Dua collection
For one afflicted with doubt in his faith
دعاء من أصابه شك في الإيمان
3 supplications
يَسْتَعِيذُ بِاللَّهِ. يَنْتَهِي عَمَّا شك فِيهِ.
(Say:) I seek refuge in Allah. (Then you should desist from doing what you are in doubt about.)
Al-Bukhari, cf. Al-Asqalani, Fathul-Bari 6/336, Muslim 1/120.
يقول" آمنت بالله ورسله"
(Say:) I believe in Allah and His Messengers.
Muslim, 1/119-20.
يقرأ قوله تعالى ((هُوَ الأوَّلُ، وَالآخِـرُ، وَالظّـاهِـرُ، وَالْبـاطِـنُ، وَهُوَ بِكُلِّ شَيءٍ عَلـيم))
(Recite the Ayat) He is the First and the Last, the Most High and the Most Near. And He is the Knower of all things (in Arabic).
Al-Hadid 57:3, Abu Dawud 4/329. Al-Albani graded it good in SahihAbu Dawud, 3/962.