Why does a Muslim say "Alhamdulillah" after sneezing?

The Sunnah of the Prophet obliges the sneezer to praise Allah, and obliges the one who hears him to say to him: "May Allah have mercy on you." The sneezer, in turn, should reply by saying: "May Allah guide you and set your affairs in order." This is because sneezing is a blessing, as it expels congested vapors, is a sign of Allah's love, and vexes Satan. For this reason, supplicating for mercy upon the sneezer is called "tashbeet" [making firm] due to its vexation of Satan. As for yawning, it is from Satan, so a Muslim should repel it as much as he can.