Allah said:

أَمْ حَسِبْتُمْ أَن تَدْخُلُواْ الْجَنَّةَ

(Or think you that you will enter Paradise) before you are tested and tried just like the nations that came before you This is why Allah said:

وَلَمَّا يَأْتِكُم مَّثَلُ الَّذِينَ خَلَوْاْ مِن قَبْلِكُم مَّسَّتْهُمُ الْبَأْسَآءُ وَالضَّرَّآءُ

(...without such (trials) as came to those who passed away before you They were afflicted with severe poverty and ailments) meaning, illnesses, pain, disasters and hardships. Ibn Mas`ud, Ibn `Abbas, Abu Al-`Aliyah, Mujahid, Sa`id bin Jubayr, Murrah Al-Hamdani, Al-Hasan, Qatadah, Ad-Dahhak, Ar-Rabi`, As-Suddi and Muqatil bin Hayyan said that

الْبَأْسَآءِ

(Al-Ba'sa') means poverty. Ibn `Abbas said that

وَالضَّرَّآءِ

(...and Ad-Darra') means ailments.

وَزُلْزِلُواْ

(and were so shaken) for fear of the enemy, and were tested, and put to a tremendous trial. An authentic Hadith narrated that Khabbab bin Al-Aratt said, "We said, `O Messenger of Allah ﷺ! Why do you not invoke Allah to support us Why do you not supplicate to Allah for us' He said:

«إِنَّ مَنْ كَانَ قَبْلَكُمْ كَانَ أَحَدُهُمْ يُوضَعُ الْمِنْشَارُ عَلى مَفْرَقِ رَأْسِهِ فَيَخْلُصُ إِلى قَدَمَيْهِ لَا يَصْرِفُهُ ذَلِكَ عَنْ دِينِهِ، وَيُمْشَطُ بِأَمْشَاطِ الْحَدِيدِ مَا بَيْنَ لَحْمِهِ وَعَظْمِهِ، لَا يَصْرِفُهُ ذلِكَ عَنْ دِينِه».

(The saw would be placed on the middle of the head of one of those who were before you (believers) and he would be sawn until his feet, and he would be combed with iron combs between his skin and bones, yet that would not make him change his religion.)

He then said:

«وَاللهِ لَيُتِمَّنَّ اللهُ هَذَا الْأَمْرَ حَتَّى يَسِيرَ الرَّاكِبُ مِنْ صَنْعَاءَ إلى حَضْرَمَوْتَ، لَا يَخَافُ إِلَّا اللهَ وَالذِّئْبَ عَلى غَنَمِهِ، وَلَكِنَّــكُمْ قَوْمٌ تَسْتَعْجِلُون»

(By Allah! This matter (religion) will spread (or expand) by Allah until the traveler leaves San`a' to Hadramawt (both in Yemen, but at a great distance from each other) fearing only Allah and then the wolf for the sake of his sheep. You are just a hasty people.)

And Allah said:

الم - ذَلِكَ الْكِتَابُ لاَ رَيْبَ فِيهِ هُدًى لِّلْمُتَّقِينَ - الَّذِينَ يُؤْمِنُونَ بِالْغَيْبِ وَيُقِيمُونَ الصَّلوةَ وَمِمَّا رَزَقْنَـهُمْ يُنفِقُونَ

(Alif-Lam-Mim. Do people think that they will be left alone because they say: "We believe," and will not be tested And We indeed tested those who were before them. And Allah will certainly make (it) known (the truth of) those who are true, and will certainly make (it) known (the falsehood of) those who are liars.) (29:1-3)

The Companions experienced tremendous trials during the battle of Al-Ahzab (the Confederates). Allah said:

إِذْ جَآءُوكُمْ مِّن فَوْقِكُمْ وَمِنْ أَسْفَلَ مِنكُمْ وَإِذْ زَاغَتِ الاٌّبْصَـرُ وَبَلَغَتِ الْقُلُوبُ الْحَنَاجِرَ وَتَظُنُّونَ بِاللَّهِ الظُّنُونَاْ - هُنَالِكَ ابْتُلِىَ الْمُؤْمِنُونَ وَزُلْزِلُواْ زِلْزَالاً شَدِيداً - وَإِذْ يَقُولُ الْمُنَـفِقُونَ وَالَّذِينَ فِى قُلُوبِهِم مَّرَضٌ مَّا وَعَدَنَا اللَّهُ وَرَسُولُهُ إِلاَّ غُرُوراً

(When they came upon you from above you and from below you, and when the eyes grew wild and the hearts reached to the throats, and you were harboring doubts about Allah. There, the believers were tried and shaken with a mighty shaking. And when the hypocrites and those in whose hearts is a disease (of doubts) said: "Allah and His Messenger promised us nothing but delusion!") (33:10-12)

When Heraclius asked Abu Sufyan, "Did you fight him (Prophet Muhammad)" He said, "Yes." Heraclius said, "What was the outcome of warfare between you" Abu Sufyan said, "Sometimes we lose and sometimes he loses." He said, "Such is the case with Prophets, they are tested, but the final victory is theirs."

Allah's statement:

مَّثَلُ الَّذِينَ خَلَوْاْ مِن قَبْلِكُم

(...without (such) (trials) as came to those who passed away before you) meaning, their way of life. Similarly, Allah said:

فَأَهْلَكْنَآ أَشَدَّ مِنْهُم بَطْشاً وَمَضَى مَثَلُ الاٌّوَّلِينَ

(Then We destroyed men stronger (in power) than these ـ and the example of the ancients has passed away (before them)) (43: 8) and:

وَزُلْزِلُواْ حَتَّى يَقُولَ الرَّسُولُ وَالَّذِينَ ءَامَنُواْ مَعَهُ مَتَى نَصْرُ اللَّهِ

(...were so shaken that even the Messenger and those who believed along with him said, "When (will come) the help of Allah.")

They pleaded (to Allah) for victory against their enemies and invoked Him for aid and deliverance from their hardships and trials. Allah said:

أَلاَ إِنَّ نَصْرَ اللَّهِ قَرِيبٌ

(Yes! Certainly, the help of Allah is near!)

Allah said:

فَإِنَّ مَعَ الْعُسْرِ يُسْراً - إِنَّ مَعَ الْعُسْرِ يُسْراً

(Verily, along with every hardship is relief. Verily, along with every hardship is relief.) (94:5, 6)

So just as there is hardship, its equal of relief will soon arrive. This is why Allah said:

أَلاَ إِنَّ نَصْرَ اللَّهِ قَرِيبٌ

(Yes! Certainly, the help of Allah is near!)