The Prophet (peace be upon him) said to his companions: Shall I not tell you some words which, if distress or grief befalls any of you and he offers this prayer, it will bring him joy?
It is the du‘a of Dhoo’l-Noon (i.e. Prophet Yunus):
لا إله إلا أنت سبحانك إني كنت من الظالمين
la ilaha illa anta , subhanak, inne kuntu min adh dhalimeen
There is no God but You, exalted are You; surely, I was one of the wrongdoers!
Source: Sahih al-Jami‘ (no. 2605)