Sura 9:122 – 125 — Repentence
[9.122] It is not right that all the faithful should go to war at once. A band from each community should stay behind to instruct themselves in religion and to admonish their men when they return, so that they may take heed.
[9.123] Believers, make war on the infidels who dwell around you. Deal firmly with them. Know that God is with the righteous.
[9.124] Whenever a Chapter is revealed, some of them ask: “Whose faith will this increase?” It will surely increase the believers' faith and give them joy. [9.125] As for those whose hearts are tainted, it will add uncleanness to their uncleanness, so that they shall die while still in unbelief.
From N. J. Dawood, The Koran (London: Penguin Books, 2003), page 146.