التوبة — At-Taubah Ayat 122
۞ وَمَا كَانَ الْمُؤْمِنُوْنَ لِيَنْفِرُوْا كَاۤفَّةًۗ فَلَوْلَا نَفَرَ مِنْ كُلِّ فِرْقَةٍ مِّنْهُمْ طَاۤىِٕفَةٌ لِّيَتَفَقَّهُوْا فِى الدِّيْنِ وَلِيُنْذِرُوْا قَوْمَهُمْ اِذَا رَجَعُوْٓا اِلَيْهِمْ لَعَلَّهُمْ يَحْذَرُوْنَ ࣖ
Wa mā kānal-mu'minūna liyanfirū kāffah(tan), falau lā nafara min kulli firqatim minhum ṭā'ifatul liyatafaqqahū fid-dīni wa liyunżirū qaumahum iżā raja‘ū ilaihim la‘allahum yaḥżarūn(a).
"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."