Musnad Ahmad 30:2040

Sulayman ibn Dawud narrated to us, Isma'il informed us, al-'Ala' informed me, from his father, from Abu Hurayrah, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Indeed, yawning is from the Shaytan. So if one of you yawns, let him suppress it as much as he is able."