Surah An-Nisa, Verse 86

وَإِذَا حُيِّيتُم بِتَحِيَّةٖ فَحَيُّواْ بِأَحۡسَنَ مِنۡهَآ أَوۡ رُدُّوهَآۗ إِنَّ ٱللَّهَ كَانَ عَلَىٰ كُلِّ شَيۡءٍ حَسِيبًا٨٦

wa-idhā ḥuyyītum bitaḥiyyatin faḥayyū bi-aḥsana min'hā aw ruddūhā inna l-laha kāna ʿalā kulli shayin ḥasīban

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 Allāh is ever, over all things, an Accountant.