النساۤء — An-Nisa' Ayat 86
وَاِذَا حُيِّيْتُمْ بِتَحِيَّةٍ فَحَيُّوْا بِاَحْسَنَ مِنْهَآ اَوْ رُدُّوْهَا ۗ اِنَّ اللّٰهَ كَانَ عَلٰى كُلِّ شَيْءٍ حَسِيْبًا
Wa iżā ḥuyyītum bitaḥiyyatin fa ḥayyū bi'aḥsana minhā au ruddūhā, innallāha kāna ‘alā kulli syai'in ḥasībā(n).
"And when you are greeted with a greeting, greet [in return] with one better than it or [at least] return it [in a like manner]. Indeed, Allah is ever, over all things, an Accountant."