The Prophet Muhammad (SAW) said: "Allah likes sneezing and dislikes yawning. When any one of you sneezes and says 'Alhamdulilah' (praise be to Allah), it becomes obligatory for every Muslim who hears him to respond 'Yarhamuk-Allah' (May Allah have mercy on you). Yawning is from the devil. When one of you feels like yawning, he should restrain it as much as possible, for the devil laughs as you when one of you yawns." - Bukhari

The Messenger of Allah (SAW) said: "When one yawns, he should put his hand over his mouth, otherwise the devil will enter." - Muslim

Sneezing lightens load and provides relief within us; something we should always praise Allah for. We should always respond to the one who sneezes a minimum of three times and avoid responding to the one who sneezes and doesn't praise Allah. Yawning on the other hand is considered a sign of gluttony and laziness. One should always attempt to cover up a yawn and not make loud noises while doing so. This is a chance to degrade Shaytan and should not be missed