Quran 9:38 — Ultimatum (Bara'ah)

O you who believe, when you are told, "Mobilize in the cause of GOD," why do you become heavily attached to the ground? Have you chosen this worldly life in place of the Hereafter? The materials of this world, compared to the Hereafter, are nil.

[9:37] Altering the Sacred Months is a sign of excessive disbelief; it augments the straying of those who have disbelieved. They alternate the Sacred Months and the regular months, while preserving the number of months consecrated by GOD. They thus violate what GOD has consecrated. Their evil works are adorned in their eyes. GOD does not guide the disbelieving people.

[9:39] Unless you mobilize, He will commit you to painful retribution and substitute other people in your place; you can never hurt Him in the least. GOD is Omnipotent.