Anas (RA) said: Two men sneezed in the presence of the prophet (peace be upon him). He said: Allah have mercy on you! To one and not to the other. He was asked: Messenger of Allah! Two persons sneezed. Ahmad’s version has: You invoked a blessing on one of them and left the other. He replied: This man praised Allah, and this man did not praise Allah.
Sunan Abi Dawud, Book 43, Hadith 267