Quran 9:42 — Ultimatum (Bara'ah)

If there were a quick material gain, and a short journey, they would have followed you. But the striving is just too much for them. They will swear by GOD: "If we could, we would have mobilized with you." They thus hurt themselves, and GOD knows that they are liars.

[9:41] You shall readily mobilize, light or heavy, and strive with your money and your lives in the cause of GOD. This is better for you, if you only knew.

[9:43] GOD has pardoned you: why did you give them permission (to stay behind), before you could distinguish those who are truthful from the liars?