What to say to the disbeliever who sneezes and praises Allah

إِنَّ ٱللَّهَ وَمَلَٰٓئِكَتَهُۥ يُصَلُّونَ عَلَى ٱلنَّبِىِّ ۚ يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ صَلُّوا۟ عَلَيْهِ وَسَلِّمُوا۟ تَسْلِيمًا

God and His angels shower their blessings on the Prophet. O believers, you should also send your blessings on him, and salute him with a worthy greeting.

Al-Ahzab 33:56