Riyad as-SalihinChapter 5Hadith 202
Full Sharh — Riyad as-Salihin 202
وعن أنس رضي الله عنه قال: عطس رجلان عند النبي صلى الله عليه وسلم ، فشمت أحدهما ولم يشمت الآخر، فقال الذي لم يشمته: عطس فلان فشمته، وعطست فلم تشمتني؟ فقال: "هذا حمد الله، وإنك لم تحمد الله" ((متفق عليه))
English Translation
Anas (May Allah be pleased with him) reported:: When two men sneezed in the presence of the Prophet (ﷺ), he responded to one with "Yarhamuk-Allah (may Allah have mercy on you)" and did not respond to the other. The latter said to him: "You invoked a blessing on this man but did not do so in my case." The Prophet (ﷺ) replied, "He praised Allah (i.e., he said 'Al-hamdu lillah') but you did not.".
Source
Riyad as-Salihin(رياض الصالحين)
The Book of Greetings
Hadith Number
202