Imām an-Nawawī, may Allāh have mercy upon him said:

It is sunnah at the time of karb (distress) and weighty matters the du’ā of karb :

لَا إلَهَ إلَّا اللَّهُ
There is no true God but Allāh
الْعَظِيمُ الْحَلِيمُ
the Incomparably Great, the Clement
لَا إلَهَ إلَّا اللَّهُ
There is no true God but Allāh
رَبُّ الْعَرْشِ الْعَظِيمِ
the Lord of the Great ‘Arsy
لَا إلَهَ إلَّا اللَّهُ
There is no true God but Allāh
رَبُّ السَّمَوَاتِ
the Lord of the Skies,
وَرَبُّ الْأَرْضِ
the Lord of the Earth,
رَبُّ الْعَرْشِ الْكَرِيمِ
and the Lord of the Glorious ‘Arsy.

And also:

يَا حَيُّ يَا قَيُّومُ
Oh the Ever Living!
Oh the Self-Subsisting by Whom all things subsists!
بِرَحْمَتِكَ أَسْتَغِيثُ
by Your Mercy I seek aid.

And also:

Oh Allāh!
رَحْمَتَكَ أرجوا
Your Mercy I hope for
فَلَا تَكِلنِي إلَى نَفْسِي
So do not leave me to myself
طَرْفَةَ عَيْنٍ
For a wink of an eye
وَأَصْلِحْ لِي شَأْنِي كُلَّهُ
And rectify for me all my affairs
لَا إلَهَ إلَّا أَنْتَ
The is no God but You.

It is mandūb in all mawţin (places):

Oh Allah!
آتِنَا فِي الدُّنْيَا حَسَنَةً
Give us hasanah in the dunyā,
وَفِي الآخِرَةِ حَسَنَةً
hasanah in the ākhirah
وَقِنَا عَذَابَ النَّارِ
and protect us from the torment of the fire.

Also the verses of Kursī, and the ending verses of al-Baqarah.

And when one fears a sultan or others, he says,

Oh Allah!
إنِّي أَعُوذُ بِكَ مِنْ شُرُورِهِمْ
surely I seek protection with you from their evils
وَأَجْعَلُكَ فِي نُحُورِهِمْ
And I let You face them.

And when shaiţān presents itself to him, he seeks Allāh’s protection from it and he recites whatever is made easy from the Qur’ān.

When something afflicts him, he should say:

قَدَّرَ اللَّهُ
Allah decreed it,
وَمَا شَاءَ اللَّهُ فَعَلَ
and whatever Allāh wills, happens.

And he should say, to avert afflictions (āfāt):

مَا شَاءَ اللَّهُ
(This is) what Allāh wills,
لَا قُوَّةَ إلَّا بِاَللَّه
there is no strength (to avert the affliction) except by Allāh.

And at the time of misfortune (muśībah),

‎إنَّا لِلَّهِ
Surely we belong to Alāh
‎وَإِنَّا إلَيْهِ رَاجِعُونَ
And surely to him we all return.

And at the time of blessing (ni’mah),

‎نَحْمَدُ اللَّهَ وَنَشْكُرُهُ
We praise Allāh and we thank Him.

And when one is in debt, he should say:

Oh Allāh!
‎اكْفِنِي بِحَلَالِكَ
Suffice us with Your Halāl (lawful)
‎ عَنْ حَرَامِك
from Your Harām (Unlawful)
‎وَأَغْنِنِي بِفَضْلِكَ
Make me sufficient with Your Fadhl (Grace)
‎عَمَّنْ سِوَاك
from anyone other than You.

When one is afflicted by wahsyah (loneliness), he should say:

‎أَعُوذُ بِكَلِمَاتِ اللَّهِ التَّامَّاتِ
I seek protection with the complete kalimahs of Allah
‎ مِنْ غَضَبِهِ وَعِقَابِهِ
From His Anger and His Punishment,
‎وَشَرِّ عِبَادِهِ
the evil of His Servants,
‎ وَمِنْ هَمَزَاتِ الشَّيَاطِينِ وَأَنْ يَحْضُرُونَ

And from the hamazāt (vain suggestions inspired to the minds of men) of the syaitān and their presence.

And when one is afflicted with waswasah (evil or unprofitable thoughts which bestirs itself in the mind), one should seek the Protection of Allāh from syaitān and he should stop it’s persistence. If the waswas occurs during ihrām for śalah, he should make ta’awwuzh of Allāh from it, and he spit on his left side three times and say:

‎لَا إلَهَ إلَّا اللَّهُ
There is no true god but Allāh.

He repeats it.

One recites to the ma’tūh (afflicted in one’s intellect), maldūgh (stung or bitten), the Fatiĥāh of the Book.

When one seeks for ta’wīzh (protection) of the śabiy (child), he says

‎أُعِيذُكَ بِكَلِمَاتِ اللَّهِ التَّامَّاتِ
I pray for your protection with Allāh’s Complete Kalimahs
‎مِنْ كُلِّ شَيْطَانٍ وَهَامَّةٍ
from all syaitān and venomous creatures
‎وَمِنْ كُلِّ عَيْنٍ لَامَّةٍ
and from every evil eye.