هُوَ الأَوَّلُ ، وَالآخِرُ ، وَالظَّاهِرُ ، وَالْبَاطِنُ ، وَهُوَ بِكُلِّ شَيْءٍ عَلِيمٌ
Translation 
If one finds something doubtful in his/her heart then he should recite the following verse:
“He (Allah) is The First and The Last, Aẓaahir and Al-Baaṭin and He knows well all things.”
Note:
Aẓaahir: Indicates the greatness of His attributes and the insignificance of every single creation in respect to His greatness and Highness, for He is above all of His creation as regards His essence and attributes.
Al-Baaṭin: Indicates His awareness and knowledge of all secrets, of that which is in the hearts and the most intimate of things just as it indicates His closeness and nearness to all in a manner which befits His majesty.
“He (Allah) is The First and The Last, Aẓaahir and Al-Baaṭin and He knows well all things.”
Note:
Aẓaahir: Indicates the greatness of His attributes and the insignificance of every single creation in respect to His greatness and Highness, for He is above all of His creation as regards His essence and attributes.
Al-Baaṭin: Indicates His awareness and knowledge of all secrets, of that which is in the hearts and the most intimate of things just as it indicates His closeness and nearness to all in a manner which befits His majesty.
Transliteration
huwal-awwalu, wal-aakhiru, waẓ-ẓaahiru, wal-baaṭinu, wa huwa bi kulli shay’in ‛aleem
Sources:
Abu Dawud No# 5110
