آمَنْـتُ بِاللهِ وَرُسُـلِه
Amantu billahi warusulih
Translation
I have believed in Allah and His Messengers.
When to recite
Recited when one is afflicted with doubts about faith. Also seek refuge in Allah and renounce the doubt.
Source / Reference
Al-Bukhari 4/149, Muslim 1/120