The Quran

يا أَيُّهَا الَّذينَ آمَنوا إِذا ضَرَبتُم في سَبيلِ اللَّهِ فَتَبَيَّنوا وَلا تَقولوا لِمَن أَلقىٰ إِلَيكُمُ السَّلامَ لَستَ مُؤمِنًا تَبتَغونَ عَرَضَ الحَياةِ الدُّنيا فَعِندَ اللَّهِ مَغانِمُ كَثيرَةٌ ۚ كَذٰلِكَ كُنتُم مِن قَبلُ فَمَنَّ اللَّهُ عَلَيكُم فَتَبَيَّنوا ۚ إِنَّ اللَّهَ كانَ بِما تَعمَلونَ خَبيرًا

Muhammad Asad

[Hence,] O you who have attained to faith, when you go forth [to war] in God's cause, use your discernment, and do not - out of a desire for the fleeting gains of this worldly life - say unto anyone who offers you the greeting of peace, "Thou art not a believer"¹ for with God there are gains abundant. You, too, were once in the same condition² - but God has been gracious unto you. Use, therefore, your discernment: verily, God is always aware of what you do.

Sc., "and therefore one of the enemies". This verse prohibits the treating of noncombatants as enemies and using their supposed unbelief as a pretext for plundering them. The injunction "use your discernment" (tabayyanu) imposes on the believers the duty of making sure, in every case, whether the persons concerned are actively engaged in hostilities or not.
Lit., "thus have you [too] been aforetime". Since the preceding injunction refers to the whole community, it would seem that the above clause, too, bears the same implication: namely, a reference to the time when the Muslim community was, because of its weakness and numerical insignificance, at the mercy of enemies endowed with greater power. Thus, the believers are told, as it were: "Remember your erstwhile weakness, and treat the peacefully-minded among your enemies with the same consideration with which you yourselves were once hoping to be treated."