Hadith - Bukhari 4:509, Narrated Abu Huraira

The Prophet said, "Yawning is from Satan and if anyone of you yawns, he should check his yawning as much as possible, for if anyone of you (during the act of yawning) should say: 'Ha', Satan will laugh at him."

Hadith - Bukhari 8:242, 8:245, Narrated Abu Huraira

The Prophet said, "Allah likes sneezing and dislikes yawning, so if someone sneezes and then praises Allah, then it is obligatory on every Muslim who heard him, to say: May Allah be merciful to you (Yar-hamuka-l-lah). But as regards yawning, it is from Satan, so one must try one's best to stop it, if one says 'Ha' when yawning, Satan will laugh at him."

Hadith - Muslim, Narrated AbuSa'id al-Khudri

Allah's Apostle said: When one of you yawns, he should try to restrain it with the help of his hand since it is the Satan that enters therein.

Hadith - Mishkat, Narrated AbuHurayrah , transmitted by Tirmidhi and Ibn Majah.

Allah's Messenger said, Yawning in prayer is an act of Shaytan, so when one of you yawns he should restrain it as much as possible. In another version it the word are: He should place his hand upon his mouth.

Hadith - Mishkat, Narrated by Grandfather of Adi ibn Thabit, Transmitted by Tirmidhi

Allah's Messenger said: Sneezing, drowsing, yawning in prayer, also menstruation, vomiting and nose-bleeding are from (the acts of) Shaytaan (Satan).  *[i.e. when they occur during salat]

Action Items for the uttaqun:

• Cover your mouth when you must yawn

Remember... Allah, subhana watala, sees everything we do!