Good Manners and Form (Al-Adab)
78/123. Chapter:
To say 'Al-Hamdu-lillah' on sneezing
Sahih Bukhari
حَدَّثَنَا مُحَمَّدُ بْنُ كَثِيرٍ، حَدَّثَنَا سُفْيَانُ، حَدَّثَنَا سُلَيْمَانُ، عَنْ أَنَسِ بْنِ مَالِكٍ ـ رضى الله عنه ـ قَالَ عَطَسَ رَجُلاَنِ عِنْدَ النَّبِيِّ صلى الله عليه وسلم فَشَمَّتَ أَحَدَهُمَا وَلَمْ يُشَمِّتِ الآخَرَ، فَقِيلَ لَهُ فَقَالَ " هَذَا حَمِدَ اللَّهَ، وَهَذَا لَمْ يَحْمَدِ اللَّهَ ".
Narrated Anas bin Malik: Two men sneezed before the Prophet. The Prophet (ﷺ) said to one of them, "May Allah bestow His Mercy on you," but he did not say that to the other. On being asked (why), the Prophet (ﷺ) said, "That one praised Allah (at the time of sneezing), while the other did not praise Allah."
Reference : Sahih al-Bukhari 6221In-book reference : Book 78, Hadith 245USC-MSA web (English) reference : Vol. 8, Book 73, Hadith 240