Hadith 881

Anas (May Allah be pleased with him) reported: When two men sneezed in the presence of the Prophet (PBUH), he responded to one with "Yarhamuk-Allah (may Allah have mercy on you)" and did not respond to the other. The latter said to him: "You invoked a blessing on this man but did not do so in my case." The Prophet (PBUH) replied, "He praised Allah (i.e., he said 'Al-hamdu lillah') but you did not."

[Al-Bukhari and Muslim].