سورة النساء

وَإِذَا حُيِّيتُمْ بِتَحِيَّةٍ فَحَيُّوا بِأَحْسَنَ مِنْهَا أَوْ رُدُّوهَا ۗ إِنَّ اللَّهَ كَانَ عَلَىٰ كُلِّ شَيْءٍ حَسِيبًا ﴿٨٦﴾

Surah an-Nisa'

86. When you are greeted with a greeting, respond with a better greeting, or return it. Allah keeps count of all things.