Surah 2. Al-Baqara, Ayah 244

I.e., in a just war in self-defence against oppression or unprovoked aggression (cf. {2:190-194}).

For God's cause we must fight, but never to satisfy our own selfish passions or greed, for the warning is repeated: "God heareth and knoweth all things" all deeds, words and motives are perfectly open before Him, however we might conceal them from men or even from ourselves. See ii. 216, n. 236.