Surah An-Nisa, verse 94

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

4:94 O you who believe, when you go to fight in the way of Allah, make sure [who you fight]; and do not say to someone who offers you the greetings of peace, “You are not a believer” – seeking gains of the life of this world, while Allah has abundant gains. You were in the same position before, then Allah blessed you [with Islam]. Therefore make sure, for Allah is All-Aware of what you do