Riyad as-Salihin 881
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." [Al-Bukhari and Muslim] .
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)‏‏)‏