لَا إِلَهَ إِلَّا اللَّهُ الْعَظِيمُ الْحَلِيمُ، لَا إِلَهَ إِلَّا اللَّهُ رَبُّ الْعَرْشِ الْعَظِيمِ، لَا إِلَهَ إِلَّا اللَّهُ رَبُّ السَّمَاوَاتِ وَرَبُّ الْأَرْضِ وَرَبُّ الْعَرْشِ الْكَرِيمِ
Transliteration
La ilaha illallahul-'azimul-halim, la ilaha illallahu Rabbul-'arshil-'azim, la ilaha illallahu Rabbus-samawati wa Rabbul-ardi wa Rabbul-'arshil-karim
English meaning
There is no deity except Allah, the Great, the Forbearing. There is no deity except Allah, Lord of the Mighty Throne. There is no deity except Allah, Lord of the heavens and earth and Lord of the noble Throne.
When is it recited?
In times of distress and grief.
Its virtue
The Prophet recited this in times of distress.
Source
Bukhari, Da'awat 27