So and so sneezed and you said: May Allah have mercy upon you. I also sneezed but you did not utter these words for me. Thereupon he (the Holy Prophet) said: That person praised Allah, and you did not praise Allah.
عَطَسَ عِنْدَ النَّبِيِّ ﷺ رَجُلاَنِ فَشَمَّتَ أَحَدَهُمَا وَلَمْ يُشَمِّتِ الآخَرَ فَقَالَ الَّذِي لَمْ يُشَمِّتْهُ عَطَسَ فُلاَنٌ فَشَمَّتَّهُ وَعَطَسْتُ أَنَا فَلَمْ تُشَمِّتْنِي قَالَ إِنَّ هَذَا حَمِدَ اللَّهَ وَإِنَّكَ لَمْ تَحْمَدِ اللَّهَ