Two men sneezed in the presence of the prophet (May 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