Good Manners and Form (Al-Adab)
78/127. Chapter:
Tashmu should not be said to a sneezer if he does not say 'Al-Hamdu-lillah'
Sahih Bukhari
حَدَّثَنَا آدَمُ بْنُ أَبِي إِيَاسٍ، حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا سُلَيْمَانُ التَّيْمِيُّ، قَالَ سَمِعْتُ أَنَسًا ـ رضى الله عنه ـ يَقُولُ عَطَسَ رَجُلاَنِ عِنْدَ النَّبِيِّ صلى الله عليه وسلم فَشَمَّتَ أَحَدَهُمَا وَلَمْ يُشَمِّتِ الآخَرَ. فَقَالَ الرَّجُلُ يَا رَسُولَ اللَّهِ شَمَّتَّ هَذَا وَلَمْ تُشَمِّتْنِي. قَالَ " إِنَّ هَذَا حَمِدَ اللَّهَ، وَلَمْ تَحْمَدِ اللَّهَ ".
Narrated Anas: Two men sneezed before the Prophet (ﷺ) and he said Tashmit to one of them, while he did not say Tashmit to the other. So that man said, "O Allah's Messenger (ﷺ)! You said Tashmit to that fellow but you did not say Tashmit to me. "The Prophet (ﷺ) said, "That man praised Allah, but you did not praise Allah."
Reference : Sahih al-Bukhari 6225In-book reference : Book 78, Hadith 249USC-MSA web (English) reference : Vol. 8, Book 73, Hadith 244