Mukhtasar Bukhari (Abridged) 1389 — Description of Iblis and his army

Narrated Abu Huraira (may Allah be pleased with him) from the Prophet (peace and blessings of Allah be upon him) that he said: "Yawning is from the devil, so when one of you feels like yawning, he should try to restrain it as much as possible, because when one of you says 'Ha' while yawning, the devil laughs."