sneezing & yawning
The Prophet said ,
``Verily, Allah loves sneezing and detests yawning; so if one of you sneezes and [then] praises Allah, it is a right upon every Muslim who hears him to say to him, `Yarhamakullah (May Allah have mercy on you).’ As for yawning, then verily, it is from the Shaitaan only; so if one of you yawns, then let him ward it off (i.e., ward off and stifle the yawn) as much as he is able to ...... "
First, The Manners Of Sneezing :
1) Saying `May Allah Have Mercy On You’
To The Person Who Sneezed
Sneezing is a blessing of Allah upon His slaves, and when one is given a blessing from Allah , he should praise Allah and thank Him for it. The matter is no different in regard to sneezing, for when a person sneezes, it is legislated for him to praise Allah , by saying, ‘‘ Alhamdulillah (All praise is to Allah).’’ Al-Baraa Ibn `Aazib said, ``The Prophet ordered us with seven [commands] and forbade us from seven [prohibited matters]: he ordered us to follow funerals (by praying the funeral prayer and then following the corpse until the burial is completed), to visit the sick, to answer (i.e., accept the invitation of) a person who invites [one to partake of a meal, for example], to help the one who is wronged, to fulfill one’s oath, to return greetings of peace, and to do Tashmeet of a person who sneezes [i.e., to say, ` Yarhamukallah (may Allah have mercy on you),’ when he says, ` Alhamdulillah (All praise is to Allah),’ after he sneezes]...’’ It is compulsory to say, `May Allah have mercy on you,’ to a person who sneezes; however, it is a compulsory duty on the group of people that hears the sneezer say, `All praise is to Allah,’ and not upon every single individual from them. What this means is that at least some of them must say, `May Allah have mercy on you,’ and that, if some of them say it, saying it is no longer compulsory on the rest of them. Though this is the ruling that scholars mention, no one should refrain from saying, `May Allah have mercy on you,’ to someone who sneezes, for the Prophet said ,
"So if one of you sneezes and [then] praises Allah, it is a right upon every Muslim who hears him to say to him, `Yarhamakullah (May Allah have mercy on you"
2)One Should Say, `May Allah Have Mercy On You,’ Only After The Sneezer Praises Allah
Anas t said, ``Two men sneezed in the presence of the Prophet ; he Shammata (i.e., said, ` Yarhamukallah - May Allah have mercy on you’) to one of them but not to the other. The [latter] man said, ‘O Messenger of Allah, you Shammatta (i.e., said, `May Allah have mercy on you’) to him but not to me?’ The Prophet said ,
"Verily, he praised Allah, and you did not praise Allah. "
And in another Hadith , Abu Moosa Al-Ash’aree t reported that he heard the Messenger of Allah r say ,
``When one of you sneezes and then praises Allah, then Shammitooh (i.e., say to him, `May Allah have mercy on you’); and if he does not praise Allah, then do not Tushamitooh (i.e., do not say to him, `May Allah have mercy on you. "(
If someone does not praise Allah the Almighty.
If someone sneezes more than three times, this shows that they have caught a cold.
It is Sunnah to restrain from yawning with the help of his hand:
What proves this is the following:
Abu Hurairah t narrated that the Prophet r 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 (Yarhamuka Allah).’ But in regards to yawning, it is from Satan, so one must try one’s best to stop it, if one says ‘Ha’ while yawning, Satan will laugh at him.’”
Imam Muslim reports through Abu Sa’id t that the Prophet r said,
“When one of you yawns, he should try to restrain it with the help of his hand lest Satan enters therein.”
Thus, one should prevent yawning either by restraining it through closing the mouth, by the hand, or the like. Ibn Hajar (may Allah have mercy on him) said, “As for yawning, it is from Satan.” Ibn Battal commented, “Attributed yawning to Satan because he loves to see man in that shape so he (i.e. Satan) would laugh at him.”
Also Ibn al-’Arabi said, “We stated that every disliked act is attributed to Satan because he is the tool and every good act has been attributed to Allah because He is the One who causes it. Yawning comes as a result of having one’s stomach full and of course this will lead to laziness. However, sneezing results from having less food which automatically leads to zeal and enthusiasm. Hence, Allah loves it.”
An-Nawawi said, “Yawning has been attributed to Satan as he (Satan) calls for desires and this results also from filling the stomach. Thus, the warning here is against the cause behind this, i.e. to replete the stomach.” 
In addition, it is better for the yawner not to raise his voice or make some sounds such as “Haa” or “Aah” while yawning as this will make Satan laugh at him.
The hadith reported by Abu Hurairah t that the Prophet r said,
“But as in regards to yawning, it is from Satan, so one must try one’s best to stop it, if one says ‘Ha’ while yawning, Satan will laugh at him.’”
The narration of Imam Ahmad (may Allah have mercy on him) states, “If one of you yawns, let him restrain it as much as he can. He should not say ‘Aah’ while he yawns as Satan will laugh at him.”
Some people are used to saying, “I ask Allah’s refuge against the devil” after yawning. It should be noted that there is no valid evidence for this saying and it is not part of the Prophet’s r Sunnah.
 Al-Bukhari no. 6223.
 Muslim no. 2992, Ahmed 4/412 no. 19696
 Al-Bukhari no. 6223
 Muslim no. 2995
 Refer to explanation of Muslim’s Sahih, Hadith no. 2994
 Al-Bukhari no. 6223, Muslim no. 2994
 Ahmad 2/429 no. 9526
Please write: COMMENT in this box to verify that you are human