Quran 4:86 from Surah An-Nisaa on Divine Marvels.
وَإِذَا حُيِّيتُم بِتَحِيَّةٖ فَحَيُّواْ بِأَحۡسَنَ مِنۡهَآ أَوۡ رُدُّوهَآۗ إِنَّ ٱللَّهَ كَانَ عَلَىٰ كُلِّ شَيۡءٍ حَسِيبًا
English translation: And when you are greeted with a greeting then greet with better than it or return it Indeed Allah is of every thing an Accountant
Transliteration: wa-idha huyyitum bitahiyyatin fahayyu bi-ahsana min'ha aw rudduha inna al-laha kana ala kulli shayin hasiban