WHEN NOT TO RESPOND TO SOMEONE WHO SNEEZES H 893 "When someone sneezes and praises Allah, you should respond with, 'May Allah have mercy on you,' but if he does not praise Allah, make no response." R 893 Muslim with a chain up to Abu Musa who related that he heard the Prophet, praise and peace be upon him, say this.
880- وعن أَبي موسى رضي الله عنه ، قَالَ : سَمِعْتُ رسول الله صلى الله عليه وآله وسلم ، يقولُ : "إِذَا عَطَسَ أحَدُكُمْ فَحَمِدَ اللهَ فَشَمِّتُوهُ ، فَإنْ لَمْ يَحْمَدِ الله فَلاَ تُشَمِّتُوهُ" رواه مسلم.