On the authority of Abu Hurayrah (may Allah be pleased with him): the Prophet (peace and blessings be upon him) said: "Indeed Allah loves sneezing and dislikes yawning. So when one of you sneezes and praises Allah the Exalted, it becomes a duty upon every Muslim who hears him to say to him: May Allah have mercy on you. As for yawning, it is only from Satan, so when one of you yawns let him suppress it as much as he can, for when one of you yawns, Satan laughs at him." Narrated by al-Bukhari.