Quran 9:122 — Ultimatum (Bara'ah)

When the believers mobilize, not all of them shall do so. A few from each group shall mobilize by devoting their time to studying the religion. Thus, they can pass the knowledge on to their people when they return, that they may remain religiously informed.

[9:121] Nor do they incur any expense, small or large, nor do they cross any valley, without having the credit written down for them. GOD will surely reward them generously for their works.

[9:123] O you who believe, you shall fight the disbelievers who attack you—let them find you stern—and know that GOD is with the righteous.