*** When one of you yawns / Jab koi Jamaae leta hai ***
Abu saeed khudhri radi allahuanhu se rivayat hai ki Rasoollallah SallallahuAlaihi wasallam ne farmaya jab koi tum mein se jamaee (yawning) le to apna haath apney munh par rakh de kyunki Shaitan (munh ke) Andar dakhil ho jata hai
Sahih Muslim, Vol 6, 7491
Abu Said al-Khudri Radi allahuanhureported that Allah’s Messenger (may peace be upon him) said: When one of you yawns, he should try to restrain it with cue help of his hand since it is the Satan that enters therein.
Sahih Muslim,Book 042, Number 7131