Surah At-Tawbah · 9:122

وَمَا كَانَ ٱلْمُؤْمِنُونَ لِيَنفِرُوا۟ كَآفَّةً ۚ فَلَوْلَا نَفَرَ مِن كُلِّ فِرْقَةٍ مِّنْهُمْ طَآئِفَةٌ لِّيَتَفَقَّهُوا۟ فِى ٱلدِّينِ وَلِيُنذِرُوا۟ قَوْمَهُمْ إِذَا رَجَعُوٓا۟ إِلَيْهِمْ لَعَلَّهُمْ يَحْذَرُونَ

“[However,] it is not necessary for the believers to march forth all at once. Only a party from each group should march forth, leaving the rest to gain religious knowledge then enlighten their people when they return to them, so that they [too] may beware [of evil].”