Read Ruku 74 of the Quran

وَمَا كَانَ لِمُؤْمِنٍ أَن يَقْتُلَ مُؤْمِنًا إِلَّا خَطَـًۭٔا ۚ وَمَن قَتَلَ مُؤْمِنًا خَطَـًۭٔا فَتَحْرِيرُ رَقَبَةٍۢ مُّؤْمِنَةٍۢ وَدِيَةٌۭ مُّسَلَّمَةٌ إِلَىٰٓ أَهْلِهِۦٓ إِلَّآ أَن يَصَّدَّقُوا۟ ۚ فَإِن كَانَ مِن قَوْمٍ عَدُوٍّۢ لَّكُمْ وَهُوَ مُؤْمِنٌۭ فَتَحْرِيرُ رَقَبَةٍۢ مُّؤْمِنَةٍۢ ۖ وَإِن كَانَ مِن قَوْمٍۭ بَيْنَكُمْ وَبَيْنَهُم مِّيثَـٰقٌۭ فَدِيَةٌۭ مُّسَلَّمَةٌ إِلَىٰٓ أَهْلِهِۦ وَتَحْرِيرُ رَقَبَةٍۢ مُّؤْمِنَةٍۢ ۖ فَمَن لَّمْ يَجِدْ فَصِيَامُ شَهْرَيْنِ مُتَتَابِعَيْنِ تَوْبَةًۭ مِّنَ ٱللَّهِ ۗ وَكَانَ ٱللَّهُ عَلِيمًا حَكِيمًۭا ﴿٩٢﴾

And never is it for a believer to kill a believer except by mistake. And whoever kills a believer by mistake - then the freeing of a believing slave and a compensation payment presented to the deceased's family [is required] unless they give [up their right as] charity. But if the deceased was from a people at war with you and he was a believer - then [only] the freeing of a believing slave; and if he was from a people with whom you have a treaty - then a compensation payment presented to his family and the freeing of a believing slave. And whoever does not find [one or cannot afford to buy one] - then [instead], a fast for two months consecutively, [seeking] acceptance of repentance from Allah. And Allah is ever Knowing and Wise.

وَمَن يَقْتُلْ مُؤْمِنًۭا مُّتَعَمِّدًۭا فَجَزَآؤُهُۥ جَهَنَّمُ خَـٰلِدًۭا فِيهَا وَغَضِبَ ٱللَّهُ عَلَيْهِ وَلَعَنَهُۥ وَأَعَدَّ لَهُۥ عَذَابًا عَظِيمًۭا ﴿٩٣﴾

But whoever kills a believer intentionally - his recompense is Hell, wherein he will abide eternally, and Allah has become angry with him and has cursed him and has prepared for him a great punishment.

يَـٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوٓا۟ إِذَا ضَرَبْتُمْ فِى سَبِيلِ ٱللَّهِ فَتَبَيَّنُوا۟ وَلَا تَقُولُوا۟ لِمَنْ أَلْقَىٰٓ إِلَيْكُمُ ٱلسَّلَـٰمَ لَسْتَ مُؤْمِنًۭا تَبْتَغُونَ عَرَضَ ٱلْحَيَوٰةِ ٱلدُّنْيَا فَعِندَ ٱللَّهِ مَغَانِمُ كَثِيرَةٌۭ ۚ كَذَٰلِكَ كُنتُم مِّن قَبْلُ فَمَنَّ ٱللَّهُ عَلَيْكُمْ فَتَبَيَّنُوٓا۟ ۚ إِنَّ ٱللَّهَ كَانَ بِمَا تَعْمَلُونَ خَبِيرًۭا ﴿٩٤﴾

O you who have believed, when you go forth [to fight] in the cause of Allah, investigate; and do not say to one who gives you [a greeting of] peace "You are not a believer," aspiring for the goods of worldly life; for with Allah are many acquisitions. You [yourselves] were like that before; then Allah conferred His favor upon you, so investigate. Indeed Allah is ever, with what you do, Acquainted.

لَّا يَسْتَوِى ٱلْقَـٰعِدُونَ مِنَ ٱلْمُؤْمِنِينَ غَيْرُ أُو۟لِى ٱلضَّرَرِ وَٱلْمُجَـٰهِدُونَ فِى سَبِيلِ ٱللَّهِ بِأَمْوَٰلِهِمْ وَأَنفُسِهِمْ ۚ فَضَّلَ ٱللَّهُ ٱلْمُجَـٰهِدِينَ بِأَمْوَٰلِهِمْ وَأَنفُسِهِمْ عَلَى ٱلْقَـٰعِدِينَ دَرَجَةًۭ ۚ وَكُلًّۭا وَعَدَ ٱللَّهُ ٱلْحُسْنَىٰ ۚ وَفَضَّلَ ٱللَّهُ ٱلْمُجَـٰهِدِينَ عَلَى ٱلْقَـٰعِدِينَ أَجْرًا عَظِيمًۭا ﴿٩٥﴾

Not equal are those believers remaining [at home] - other than the disabled - and the mujahideen, [who strive and fight] in the cause of Allah with their wealth and their lives. Allah has preferred the mujahideen through their wealth and their lives over those who remain [behind], by degrees. And to both Allah has promised the best [reward]. But Allah has preferred the mujahideen over those who remain [behind] with a great reward -

دَرَجَـٰتٍۢ مِّنْهُ وَمَغْفِرَةًۭ وَرَحْمَةًۭ ۚ وَكَانَ ٱللَّهُ غَفُورًۭا رَّحِيمًا ﴿٩٦﴾

Degrees [of high position] from Him and forgiveness and mercy. And Allah is ever Forgiving and Merciful.