Sura al-Nisāʾ 4:86

وَإِذَا حُيِّيتُم بِتَحِيَّةٍ فَحَيُّوا۟ بِأَحْسَنَ مِنْهَآ أَوْ رُدُّوهَآ إِنَّ ٱللَّـهَ كَانَ عَلَىٰ كُلِّ شَىْءٍ حَسِيبًا

wa-idhā ḥuyyītum bi-taḥiyyatin fa-ḥayyū bi-aḥsana minhā aw ruddūhā inna allāha kāna ʿalā kulli shayʾin ḥasīban

When a (courteous) greeting is offered you, meet it with a greeting still more courteous, or (at least) of equal courtesy. Allah takes careful account of all things.