Ibn 'Abbas (RA) said: The Messenger of Allah (ﷺ) used to say these words in times of danger or hardship:

لَا إِلَهَ إِلَّا اللَّهُ، الْعَظِيْمُ الْحَلِيْمُ لَا إِلَهَ إِلَّا اللَّهُ، رَبُّ الْعَرْشِ الْعَظِيْمِ لَا إِلَهَ إِلَّا اللَّهُ، رَبُّ السَّمَاوَاتِ، وَرَبُّ الْأَرْضِ، وَرَبُّ الْعَرْشِ الْكَرِيمِ

Laa 'ilaaha 'illAllaahul-'Adheemul-Haleem, laa 'ilaaha 'illAllaahu Rabbul-'Arshil-'Adheem, laa 'ilaaha 'illAllaahu Rabbus-samaawaati wa Rabbul-'ardhi wa Rabbul-'Arshil-Kareem

There is none worthy of worship but Allah the Mighty, the Forbearing. There is none worthy of worship but Allah, Lord of the Magnificent Throne. There is none worthy of worship but Allah, Lord of the heavens and Lord of the earth, and Lord of the Noble Throne.

Reference: Bukhari 7431