At a time of distress
لاَ إِلَهَ إِلاَّ اللَّهُ الْعَظِيمُ الْحَلِيمُ لاَ إِلَهَ إِلاَّ اللَّهُ رَبُّ الْعَرْشِ الْعَظِيمِ لاَ إِلَهَ إِلاَّ اللَّهُ رَبُّ السَّمَوَاتِ وَرَبُّ الأَرْضِ وَرَبُّ الْعَرْشِ الْكَرِيمِ
Transliteration
Laa ilaha illallahul-'Atheemul-Haleem, laa ilaha illallahu Rabbul-'Arshil-'Atheem, laa ilaha illallahu Rabbus-samaawaati wa Rabbul-ardi wa Rabbul-'Arshil-Kareem.
Translation
There is no god but Allah, the Great, the Tolerant, there is no god but Allah, the Lord of the Magnificent Throne There is no god but Allah, the Lord of the Heaven and the earth, the Lord of the Edifying Throne
How
The Prophet used to say this at a time of distress.
Source: Sahih Muslim 2730. Full details