Riyad as-Salihin 880
Abu Musa (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) said, "When one of you sneezes and praises Allah (i.e., says Al-hamdu lillah), you should invoke Allah's Mercy upon him (i.e., say Yarhamuk-Allah); but if he does not praise Allah, you should not respond." [Muslim] .
وعن أبي موسي رضي الله عنه قال‏:‏ سمعت رسول الله صلى  الله عليه وسلم  يقول‏:‏ ‏
"‏إذا عطس أحدكم فحمد الله فشمتوه، فإن لم يحمد الله فلا تشمتوه‏"‏ ‏(‏‏(‏رواه مسلم‏)‏‏)‏‏.‏