Read Page 70 of the Quran

ثُمَّ أَنزَلَ عَلَيْكُم مِّنۢ بَعْدِ ٱلْغَمِّ أَمَنَةًۭ نُّعَاسًۭا يَغْشَىٰ طَآئِفَةًۭ مِّنكُمْ ۖ وَطَآئِفَةٌۭ قَدْ أَهَمَّتْهُمْ أَنفُسُهُمْ يَظُنُّونَ بِٱللَّهِ غَيْرَ ٱلْحَقِّ ظَنَّ ٱلْجَـٰهِلِيَّةِ ۖ يَقُولُونَ هَل لَّنَا مِنَ ٱلْأَمْرِ مِن شَىْءٍۢ ۗ قُلْ إِنَّ ٱلْأَمْرَ كُلَّهُۥ لِلَّهِ ۗ يُخْفُونَ فِىٓ أَنفُسِهِم مَّا لَا يُبْدُونَ لَكَ ۖ يَقُولُونَ لَوْ كَانَ لَنَا مِنَ ٱلْأَمْرِ شَىْءٌۭ مَّا قُتِلْنَا هَـٰهُنَا ۗ قُل لَّوْ كُنتُمْ فِى بُيُوتِكُمْ لَبَرَزَ ٱلَّذِينَ كُتِبَ عَلَيْهِمُ ٱلْقَتْلُ إِلَىٰ مَضَاجِعِهِمْ ۖ وَلِيَبْتَلِىَ ٱللَّهُ مَا فِى صُدُورِكُمْ وَلِيُمَحِّصَ مَا فِى قُلُوبِكُمْ ۗ وَٱللَّهُ عَلِيمٌۢ بِذَاتِ ٱلصُّدُورِ ﴿١٥٤﴾

Then after distress, He sent down upon you security [in the form of] drowsiness, overcoming a faction of you, while another faction worried about themselves, thinking of Allah other than the truth - the thought of ignorance, saying, "Is there anything for us [to have done] in this matter?" Say, "Indeed, the matter belongs completely to Allah." They conceal within themselves what they will not reveal to you. They say, "If there was anything we could have done in the matter, some of us would not have been killed right here." Say, "Even if you had been inside your houses, those decreed to be killed would have come out to their death beds." [It was] so that Allah might test what is in your breasts and purify what is in your hearts. And Allah is Knowing of that within the breasts.

إِنَّ ٱلَّذِينَ تَوَلَّوْا۟ مِنكُمْ يَوْمَ ٱلْتَقَى ٱلْجَمْعَانِ إِنَّمَا ٱسْتَزَلَّهُمُ ٱلشَّيْطَـٰنُ بِبَعْضِ مَا كَسَبُوا۟ ۖ وَلَقَدْ عَفَا ٱللَّهُ عَنْهُمْ ۗ إِنَّ ٱللَّهَ غَفُورٌ حَلِيمٌۭ ﴿١٥٥﴾

Indeed, those of you who turned back on the day the two armies met, it was Satan who caused them to slip because of some [blame] they had earned. But Allah has already forgiven them. Indeed, Allah is Forgiving and Forbearing.

يَـٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ لَا تَكُونُوا۟ كَٱلَّذِينَ كَفَرُوا۟ وَقَالُوا۟ لِإِخْوَٰنِهِمْ إِذَا ضَرَبُوا۟ فِى ٱلْأَرْضِ أَوْ كَانُوا۟ غُزًّۭى لَّوْ كَانُوا۟ عِندَنَا مَا مَاتُوا۟ وَمَا قُتِلُوا۟ لِيَجْعَلَ ٱللَّهُ ذَٰلِكَ حَسْرَةًۭ فِى قُلُوبِهِمْ ۗ وَٱللَّهُ يُحْىِۦ وَيُمِيتُ ۗ وَٱللَّهُ بِمَا تَعْمَلُونَ بَصِيرٌۭ ﴿١٥٦﴾

O you who have believed, do not be like those who disbelieved and said about their brothers when they traveled through the land or went out to fight, "If they had been with us, they would not have died or have been killed," so Allah makes that [misconception] a regret within their hearts. And it is Allah who gives life and causes death, and Allah is Seeing of what you do.

وَلَئِن قُتِلْتُمْ فِى سَبِيلِ ٱللَّهِ أَوْ مُتُّمْ لَمَغْفِرَةٌۭ مِّنَ ٱللَّهِ وَرَحْمَةٌ خَيْرٌۭ مِّمَّا يَجْمَعُونَ ﴿١٥٧﴾

And if you are killed in the cause of Allah or die - then forgiveness from Allah and mercy are better than whatever they accumulate [in this world].