Allah is sufficient for us and (He is) the best Disposer of Affairs حسبي الله ونعم الوكيل

This blessed word is said in two situations:

For the first situation, Allah ﷻ said :

وَلَوْ أَنَّهُمْ رَضُوا۟ مَآ ءَاتَىٰهُمُ ٱللَّهُ وَرَسُولُهُۥ وَقَالُوا۟ حَسْبُنَا ٱللَّهُ سَيُؤْتِينَا ٱللَّهُ مِن فَضْلِهِۦ وَرَسُولُهُۥٓ إِنَّآ إِلَى ٱللَّهِ رَٰغِبُونَ

If only they had been content with what Allah and His Messenger had given them and said, “Allah is sufficient for us! Allah will grant us out of His bounty, and so will His Messenger. To Allah ˹alone˺ we turn with hope.” (Tawbah - 59)

In the second situation, Allah ﷻ said : 

ٱلَّذِينَ قَالَ لَهُمُ ٱلنَّاسُ إِنَّ ٱلنَّاسَ قَدْ جَمَعُوا۟ لَكُمْ فَٱخْشَوْهُمْ فَزَادَهُمْ إِيمَـٰنًۭا وَقَالُوا۟ حَسْبُنَا ٱللَّهُ وَنِعْمَ ٱلْوَكِيلُ 

فَٱنقَلَبُوا۟ بِنِعْمَةٍۢ مِّنَ ٱللَّهِ وَفَضْلٍۢ لَّمْ يَمْسَسْهُمْ سُوٓءٌۭ وَٱتَّبَعُوا۟ رِضْوَٰنَ ٱللَّهِ ۗ وَٱللَّهُ ذُو فَضْلٍ عَظِيمٍ

Those who were warned, “Your enemies have mobilised their forces against you, so fear them,” the warning only made them grow stronger in faith and they replied, “Allah ˹alone˺ is sufficient ˹as an aid˺ for us and ˹He˺ is the best Protector.” So they returned with Allah’s favors and grace, suffering no harm. For they sought to please Allah. And surely Allah is ˹the˺ Lord of infinite bounty. (Ali Imra - 173/174)

And these two situations are gathered in Allah's verse ﷻ : 

وَلَئِن سَأَلْتَهُم مَّنْ خَلَقَ ٱلسَّمَـٰوَٰتِ وَٱلْأَرْضَ لَيَقُولُنَّ ٱللَّهُ ۚ قُلْ أَفَرَءَيْتُم مَّا تَدْعُونَ مِن دُونِ ٱللَّهِ إِنْ أَرَادَنِىَ ٱللَّهُ بِضُرٍّ هَلْ هُنَّ كَـٰشِفَـٰتُ ضُرِّهِۦٓ أَوْ أَرَادَنِى بِرَحْمَةٍ هَلْ هُنَّ مُمْسِكَـٰتُ رَحْمَتِهِۦ ۚ قُلْ حَسْبِىَ ٱللَّهُ ۖ عَلَيْهِ يَتَوَكَّلُ ٱلْمُتَوَكِّلُونَ

If you ask them ˹O Prophet˺ who created the heavens and the earth, they will certainly say, “Allah!” Ask ˹them˺, “Consider then whatever ˹idols˺ you invoke besides Allah: if it was Allah’s Will to harm me, could they undo that harm? Or if He willed ˹some˺ mercy for me, could they withhold His mercy?” Say, “Allah is sufficient for me. In Him ˹alone˺ the faithful put their trust.” (Az-Zumar - 38)

i.e.: Say: "Allah is sufficient for me" to obtain benefits and repel misfortunes and trials.

Shaykh  'Abder Razzâq Al 'Abbâd Al Badr -  الشيخ عبد الرزاق بن عبد المحسن العباد البدر