﴿ ۞ وَمَا كَانَ ٱلْمُؤْمِنُونَ لِيَنفِرُوا۟ كَآفَّةًۭ ۚ فَلَوْلَا نَفَرَ مِن كُلِّ فِرْقَةٍۢ مِّنْهُمْ طَآئِفَةٌۭ لِّيَتَفَقَّهُوا۟ فِى ٱلدِّينِ وَلِيُنذِرُوا۟ قَوْمَهُمْ إِذَا رَجَعُوٓا۟ إِلَيْهِمْ لَعَلَّهُمْ يَحْذَرُونَ ﴾

“With all this, it is not desirable that all of the believers take the field [in time of war]. From within every group in their midst, some shall refrain from going forth to war, and shall devote themselves [instead] to acquiring a deeper knowledge of the Faith. and [thus be able to] teach their home-coming brethren, so that these [too] might guard themselves against evil.”

(And the believers should not all go out to fight�) [9:122]. Al-Kalbi reported that Ibn �Abbas said: �When Allah, exalted is He, revealed the defects of the hypocrites due to their failure to join Jihad, the believers said: �By Allah, we will never fail to join any military conquest or expedition undertaken by the Messenger of Allah, Allah bless him and give him peace�. So when the Messenger of Allah, Allah bless him and give him peace, ordered the march of military expeditions to fight the enemy, all the Muslims went out to fight and left the Messenger of Allah, Allah bless him and give him peace, alone in Medina. Allah, exalted is He, then revealed this verse�.