Remember Allah in times of ease, and Allah will remember you in times of distress

Remember that with Allah are the keys of the unseen, and He, the Almighty, All-Merciful, is the One Who brings relief from worry and distress. So turn to Him and call upon Him, and always repeat this duá:

اللَّهُمَّ إنِّي أعُوذُ بِكَ مِنَ الْهَمِّ وَ الْحَزَنِ ، وَ الْعَجْزِ وَ الْكَسَلِ ، وَ الْبُخْلِ وَ الْجُبْنِ ، وَ ضَلَعِ الدِّيْنِ وَ غَلَبَةِ الرِّجَالِ

O' Allah, I seek refuge with You from distress and grief, and I seek refuge with you from incapacity and laziness, and I seek refuge with You from miserliness and cowardice, and I seek refuge in You from the burden of debt and from being over-powered by men.

Beware of despair and frustration, recite:

لا حول ولاقوة إلا بالله

There is no power and no strength except with Allah.

These great words are the secret of happiness and success. Recite them a great deal, chase away the specters of grief and distress with them, and recive the glad tidings that Allah will soon grant you happiness and a way out.

When anxiety rears its head, worries come along and a crisis overwhelms man, making him feel that there is no way out and he is helpless, he cries out:

لَآ إِلَهَ اِ لَّا اللهُ الْعَظِيمُ الْحَلِيمُ ، لَآ إِلَهَ إ لَّا اللهُ رَبُّ الْعَرْشِ الْعَظِيمِ لَآ إِلَه ا لَّا اللهُ رَبُّ السَّمَاوَاتِ وَرَبُّ الْأَرْضِ وَرَبَّ الْعَرْشِ الْكَرِيمِ

There is no god but Allah, the Mighty, the Forbearing, there is no god but Allah, the Lord of the mighty throne, there is no god but Allah, the Lord of the heavens and the earth, and the Lord of the throne of honor.

Then his worry is dispelled and he is relieved of distress.

Saddness, grief and worry are punishments for sins that you have committed, by falling short in your prayers, or backbiting about a Muslim, or taking the matter of Hijab lightly, or committing a haraam action. Turning to Allah requires a person to renew himself, reorganize his life, develop a better relationship with his Lord and do better deeds. It is the start of a new convenant that is summed up in the following duá:

اللَّهُمَّ أَنْتَ رَبِّي لا إِلَهَ إِلا أَنْتَ خَلَقْتَنِي وَأَنَا عَبْدُكَ وَأَنَا عَلَى عَهْدِكَ وَوَعْدِكَمَا اسْتَطَعْتُ أَعُوذُ بِكَ مِنْ شَرِّ مَا صَنَعْتُ أَبُوءُ لَكَ بِنِعْمَتِكَ عَلَيَّ وَأَبُوءُ لَكَ بِذَنْبِي فَاغْفِرْ لِي فَإِنَّهُ لا يَغْفِرُ الذُّنُوبَ إِلا أَنْتَ
O Allah! You are my Lord! None has the right to be worshipped but You. You created me and I am Your slave, and I am faithful to my covenant and my promise as much as I can. I seek refuge with You from all the evil I have done. I acknowledge before You all the blessings You have bestowed upon me, and I confess to You all my sins. So I entreat You to forgive my sins, for nobody can forgive sins except You.

And Allah tells us that Dhu an-Nun (Jonah) called out:

لَّا إِلَهَ إِلَّا أَنتَ سُبْحَانَكَ إِنِّي كُنتُ مِنَ الظَّالِمِينَ 

None has the right to be worshipped but You, O' Allah, glorified and exalted be You. Truly, I have been of the wrongdoers. (Qurán 21:87)

Allah says in the Qurán:

فَاذْكُرُونِي أَذْكُرْكُمْ وَاشْكُرُواْ لِي وَلاَ تَكْفُرُونِ
So remember ' Me and I will remember you, and give thanks to Me and be not ungrateful.  (Qurán 2:152)

Remember Allah in times of ease, and He will remember you in times of distress. What hit you could not have missed you, what missed you could not have hit you. Remember that victory comes with patience, relief comes with affliction and ease comes with hardship.

(Taken from: "You can be the happiest woman in the world" by Dr. Áid al-Qarni)