وَمَا كَانَ الۡمُؤۡمِنُوۡنَ لِيَنۡفِرُوۡا كَآفَّةًؕ فَلَوۡلَا نَفَرَ مِنۡ كُلِّ فِرۡقَةٍ مِّنۡهُمۡ طَآئِفَةٌ لِّيَتَفَقَّهُوۡا فِي الدِّيۡنِ وَلِيُنۡذِرُوۡا قَوۡمَهُمۡ اِذَا رَجَعُوۡ٘ا اِلَيۡهِمۡ لَعَلَّهُمۡ يَحۡذَرُوۡنَࣖ‏

And it is not for the believers to go forth [to battle] all at once. For there should separate from every division of them a group [remaining] to obtain understanding in the religion and warn their people when they return to them that they might be cautious