An-Nisa 4:94

يَـٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوٓاْ إِذَا ضَرَبۡتُمۡ فِي سَبِيلِ ٱللَّهِ فَتَبَيَّنُواْ وَلَا تَقُولُواْ لِمَنۡ أَلۡقَىٰٓ إِلَيۡكُمُ ٱلسَّلَٰمَ لَسۡتَ مُؤۡمِنٗا تَبۡتَغُونَ عَرَضَ ٱلۡحَيَوٰةِ ٱلدُّنۡيَا فَعِندَ ٱللَّهِ مَغَانِمُ كَثِيرَةٞۚ كَذَٰلِكَ كُنتُم مِّن قَبۡلُ فَمَنَّ ٱللَّهُ عَلَيۡكُمۡ فَتَبَيَّنُوٓاْۚ إِنَّ ٱللَّهَ كَانَ بِمَا تَعۡمَلُونَ خَبِيرٗا 94

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