Musnad Ahmad 30:481

'Abd al-Razzaq narrated to us, Sufyan informed us, from Muhammad ibn 'Ajlan, from Sa'id al-Maqburi, from Abu Hurayrah, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Indeed, Allah loves sneezing, and He dislikes or hates yawning. So if one of you says: 'Ha, ha,' then that is only the devil laughing from within his belly."