another believer inconceivable unless by mistake

وَمَا كَانَ لِمُؤْمِنٍ أَن يَقْتُلَ مُؤْمِنًا إِلَّا خَطَـًٔا ۚ وَمَن قَتَلَ مُؤْمِنًا خَطَـًٔا فَتَحْرِيرُ رَقَبَةٍ مُّؤْمِنَةٍ وَدِيَةٌ مُّسَلَّمَةٌ إِلَىٰٓ أَهْلِهِۦٓ إِلَّآ أَن يَصَّدَّقُوا۟ ۚ فَإِن كَانَ مِن قَوْمٍ عَدُوٍّ لَّكُمْ وَهُوَ مُؤْمِنٌ فَتَحْرِيرُ رَقَبَةٍ مُّؤْمِنَةٍ ۖ وَإِن كَانَ مِن قَوْمٍۭ بَيْنَكُمْ وَبَيْنَهُم مِّيثَـٰقٌ فَدِيَةٌ مُّسَلَّمَةٌ إِلَىٰٓ أَهْلِهِۦ وَتَحْرِيرُ رَقَبَةٍ مُّؤْمِنَةٍ ۖ فَمَن لَّمْ يَجِدْ فَصِيَامُ شَهْرَيْنِ مُتَتَابِعَيْنِ تَوْبَةً مِّنَ ٱللَّهِ ۗ وَكَانَ ٱللَّهُ عَلِيمًا حَكِيمًا

Never should a believer kill another believer, except by mistake. If anyone kills a believer by mistake he must free one Muslim slave and pay compensation to the victim’s relatives, unless they charitably forgo it; if the victim belonged to a people at war with you but is a believer, then the compensation is only to free a believing slave; if he belonged to a people with whom you have a treaty, then compensation should be handed over to his relatives, and a believing slave set free. Anyone who lacks the means to do this must fast for two consecutive months by way of repentance to God: God is all knowing, all wise.

هُمُ ٱلَّذِينَ كَفَرُوا۟ وَصَدُّوكُمْ عَنِ ٱلْمَسْجِدِ ٱلْحَرَامِ وَٱلْهَدْىَ مَعْكُوفًا أَن يَبْلُغَ مَحِلَّهُۥ ۚ وَلَوْلَا رِجَالٌ مُّؤْمِنُونَ وَنِسَآءٌ مُّؤْمِنَـٰتٌ لَّمْ تَعْلَمُوهُمْ أَن تَطَـُٔوهُمْ فَتُصِيبَكُم مِّنْهُم مَّعَرَّةٌۢ بِغَيْرِ عِلْمٍ ۖ لِّيُدْخِلَ ٱللَّهُ فِى رَحْمَتِهِۦ مَن يَشَآءُ ۚ لَوْ تَزَيَّلُوا۟ لَعَذَّبْنَا ٱلَّذِينَ كَفَرُوا۟ مِنْهُمْ عَذَابًا أَلِيمًا

They were the ones who disbelieved, who barred you from the Sacred Mosque, and who prevented the offering from reaching its place of sacrifice. If there had not been among them, unknown to you, believing men and women whom you would have trampled underfoot, inadvertently incurring guilt on their account- God brings whoever He will into His mercy- if the [believers] had been clearly separated, We would have inflicted a painful punishment on the disbelievers.