Hadith 921
Abu Huraira (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Sneezing is from Allah and yawning is from Satan. Therefore, when any one of you feels like yawning, he should not say 'Haah', because (by this) Satan laughs in his belly."
Hadith 922
Abu Huraira (may Allah be pleased with him) narrates that the Messenger of Allah (peace be upon him) said: "Indeed, Allah likes sneezing and dislikes yawning. So when any one of you yawns, he should not make the sound 'Ah, Ah,' because Satan laughs at this, or he (the Prophet) said: 'He plays with him because of it.'"