يَٰٓأَيُّهَا 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
Yaaa aiyuhal lazeena aamanoo izaa darabtum fee sabeelil laahi fatabaiyanoo wa laa taqooloo liman alqaaa ilaikumus salaama lasta mu'minan tabtaghoona 'aradal hayaatid dunyaa fa'indal laahi maghaanimu kaseerah; kazaalika kuntum min qablu famannnal laahu 'alaikum fatabaiyanoo; innallaaha kaana bimaa ta'maloona Khabeeraa
O ye who believe! When ye go abroad in the cause of Allah, investigate carefully, and say not to any one who offers you a salutation: "Thou art none of a believer!" Coveting the perishable goods of this life: with Allah are profits and spoils abundant. Even thus were ye yourselves before, till Allah conferred on you His favours: Therefore carefully investigate. For Allah is well aware of all that ye do.
— An-Nisa' (ٱلنِّسَاء), 4:94