4:86
وَإِذَا حُيِّيتُم بِتَحِيَّةٍۢ فَحَيُّوا۟ بِأَحْسَنَ مِنْهَآ أَوْ رُدُّوهَآ ۗ إِنَّ ٱللَّهَ كَانَ عَلَىٰ كُلِّ شَىْءٍ حَسِيبًا
Wa izaa huyyeetum bitahiy yatin fahaiyoo bi ahsana minhaaa aw ruddoohaa; innal laaha kaana 'alaa kulli shai'in Haseeba
When you are greeted with a salutation then return it with a better one, or at least the same. Surely Allah takes good count of everything.
