The Quran

سَتَجِدونَ آخَرينَ يُريدونَ أَن يَأمَنوكُم وَيَأمَنوا قَومَهُم كُلَّ ما رُدّوا إِلَى الفِتنَةِ أُركِسوا فيها ۚ فَإِن لَم يَعتَزِلوكُم وَيُلقوا إِلَيكُمُ السَّلَمَ وَيَكُفّوا أَيدِيَهُم فَخُذوهُم وَاقتُلوهُم حَيثُ ثَقِفتُموهُم ۚ وَأُولٰئِكُم جَعَلنا لَكُم عَلَيهِم سُلطانًا مُبينًا

Muhammad Asad

You will find [that there are] others who would like to be safe from you as well as safe from their own folk, [but who,] whenever they are faced anew with temptation to evil, plunge into it headlong.¹ Hence, if they do not let you be, and do not offer you peace, and do not stay their hands, seize them and slay them whenever you come upon them: for it is against these that We have clearly empowered you [to make war].²

Lit., "whenever they are returned to temptation (fitnah), they are thrown back into it" or thrown headlong into it".
Lit., "that We have given you clear authority (sultan)" - a solemn reiteration of the ordinance which permits war only in self-defence (cf. 2:190 ff. as well as the corresponding notes).