لَا إِلَهَ إِلَّا أَنْتَ سُبْحَانَكَ إِنِّي كُنْتُ مِنَ الظَّالِمِينَ
Transliteration
La ilaha illa anta subhanaka inni kuntu minaz-zalimin
English meaning
There is no deity except You; exalted are You. Indeed, I have been of the wrongdoers.
When is it recited?
Can be recited during distress and at any time.
Its virtue
The supplication of Prophet Yunus from inside the whale. No Muslim makes this supplication without it being answered.
Source
Al-Anbiya 21:87