Tirmidhi

1:
And if it is not possible to stop it, then place the hand over the mouth.
It is said:
Placing the hand is also an attempt to stop it,
which is what is commanded in the hadith.

Hadith Commentary:
It is understood that when yawning, one should, as much as possible, keep one's mouth closed and not let any sound come out, because this is a sign of laziness.

Hadith Commentary:
The reality of yawning is that it is a breath due to which the mouth begins to open forcefully, so that it may expel the vapors trapped between the jaws, which are produced from the stomach being overly filled and the body becoming heavy.
The Messenger of Allah (sallallahu alayhi wa sallam) instilled aversion to it because of the cause that brings it about.
It should be noted that due to abundance in eating and drinking, a person’s body becomes heavy, and then he falls prey to laziness.
After that, the worship of Allah feels burdensome, which is why the Messenger of Allah (sallallahu alayhi wa sallam) attributed it to Shaytan, because he inclines one towards the desires and lusts of the self (nafs).
When a person is confronted with such a state, he should restrain it as much as possible; if he cannot restrain it, then he should place his hand over his mouth.
To yawn with the mouth left open and to make “ha, ha” sounds is contrary to human dignity.

Hadith Commentary:
Vocabulary of the Hadith:
Falyakzim:
He should restrain it.
Kazm means to restrain.

Benefits and Issues:
Yawning is a sign of excessive eating or overeating, and of laziness and sluggishness.
If it is not restrained,
then the appearance and shape of a person’s mouth looks unsightly, and by opening the mouth, a fly or something similar may enter it.
For this reason, it has been deemed disliked, and emphasis has been placed on restraining it.
Therefore, one should not give Satan an opportunity to be pleased or to laugh,
rather, one should close the mouth,
or place a hand over it.

Benefits and Issues:
➊ (Lā ya‘wī)
means that one should not make a sound like an animal (such as a dog or a wolf).
This word is also not narrated with an authentic chain, but the overall meaning of the hadith is established from authentic ahadith.

➋
One should try to suppress a yawn,
so that an inappropriate sound does not come out. The Prophetic instruction is:
“Yawning is from Shaytan.
He should suppress it as much as possible, because when he (the one yawning) says ‘ha’, Shaytan laughs at him.” (Sahih al-Bukhari, Book of Manners, Chapter: If one yawns, he should put his hand over his mouth, Hadith: 6226)

➌
The reason for Shaytan’s laughter is either to mock the person,
or he laughs out of happiness,
because yawning is a sign of laziness and sluggishness, which Shaytan likes.
This is because, due to laziness, a person is deprived of many good deeds.

Lexical Explanation:
«اَلتَّثَاؤُبُ» is with a hamzah. The meaning of «التثاؤب» is: to open the mouth in order to expel the vapors and gases that accumulate in the muscles of the heart so that they may be released.
«مِنَ الشَّيْطَانِ» Yawning is from Shaytan because yawning arises due to the stomach being full, the body becoming sluggish and heavy, and the senses becoming clouded, which leads to poor understanding, laziness, and sleepiness. All these things are desirable and liked by Shaytan; for this reason, it has been said that yawning is a satanic act.
«فَلْيَكْظِمْ» The ya of the imperfect verb has a fatha, and the "kha" has a kasrah beneath it, meaning: he should restrain it, hold it back, keep both lips closed to prevent it, or place his hand over his mouth.

Benefits and Issues:
➊ Yawning is the result of laziness, indolence, and filling the stomach. Shaytan is pleased when he sees a servant in such a state.
➋ It is mentioned in Sahih Bukhari that one should not say "Ha" (i.e., not make a sound), as this pleases Shaytan. [صحيح البخاري، الادب، باب ما يستحب من العطاس، وما يكره من التثاؤب، حديث: 6223]