Musnad Ahmad 30:3576

Ad-Dahhak narrated to us, Ibn ‘Ajlan narrated to us, from Sa’id, from Abu Hurairah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, Allah loves sneezing and dislikes yawning. So if one of you yawns and says, 'Ha,' then that is the devil laughing from within him."