The Book Pertaining to Piety and Softening of Hearts (Kitab Al-Zuhd wa Al-Raqa'iq)

Muslim :: Book 42 : Hadith 7131

The son of Abu Said al-Khudri reported on the authority of his father 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.