Bukhari

Hadith Commentary:
When, instead of words of gratitude, a word of ingratitude came from the mouth of the old man, the Prophet sallallahu alayhi wa sallam also said likewise, and what he said is exactly what happened.
On one hand, observe the noble character of the Prophet sallallahu alayhi wa sallam: he went to visit a Bedouin who was ill and honored him with his pure supplications.
It is true:
﴿وَإِنَّكَ لَعَلَى خُلُقٍ عَظِيمٍ﴾

Hadith Commentary:
(1)
Since that Bedouin was unfamiliar with social etiquette, the answer he gave reflects his rough temperament.
The Messenger of Allah (sallallahu alayhi wa sallam) said:
“If this is your assumption, then it will soon be fulfilled.”
Accordingly, in some narrations it is explicitly mentioned that he passed away the next morning.
(Fath al-Bari: 10/148) (2)
The commentator of Sahih al-Bukhari, Muhallab, said:
The imam should keep informed about his subordinates and not be negligent in visiting the sick, even if they are hard-hearted.
This also contains encouragement to show care and support for the members of one’s household.
Similarly, a scholar should visit the ignorant when they are ill and offer them admonition and advice from which they may benefit, and also instruct them to be patient so that they do not consider the illness to be something evil.
Otherwise, by uttering inappropriate words, Allah ta‘ala may become displeased.
The sick person should also refrain from uttering such words out of agitation that would reveal his impatience.
(‘Umdat al-Qari: 14/652)

Hadith Commentary:

It was necessary for the old man to have faith in the glad tidings given by the Messenger of Allah (sallallahu alayhi wa sallam), but contrary words came from his tongue. The Prophet (sallallahu alayhi wa sallam), seeing his despair, said, "Then it will be as you think." Accordingly, that is what happened and death came to him. Despair, in every circumstance, is disbelief (kufr). May Allah, the Exalted, protect every Muslim from despair. Ameen.

Hadith Commentary:
The Messenger of Allah (sallallahu alayhi wa sallam) comforted this elderly man, and in this there was also glad tidings for him that he would be cured of his illness. If he was not cured, then at the very least it would be an expiation for his sins. However, in a state of despair, he uttered words to the contrary, so the Messenger of Allah (sallallahu alayhi wa sallam) said:
“Then it will be as you thought.” Thus, it happened exactly so, and the next day he passed away.

Hadith Commentary:
In the narration of Tabarani, it is stated that the Messenger of Allah (sallallahu alayhi wa sallam) said: "When you do not accept our word, then it will be as you think, and Allah’s command will surely come to pass."
Then, before the next day’s evening had even arrived, he departed from this world.

Hadith Commentary:
1.
The Messenger of Allah (sallallahu alayhi wa sallam) explained this in relation to Allah’s will, that this illness will purify you from sins.
But the Bedouin considered this unlikely, so the Messenger of Allah (sallallahu alayhi wa sallam) said:
“If you do not believe what we have said, then it will be as you think; Allah’s command regarding you will certainly be fulfilled.”
Thus, the next day had not even reached evening before he passed away from this world.
(al-Mu‘jam al-Kabir by al-Tabarani: 7/306, no. 7213; Fath al-Bari: 6/763)
From this hadith, it is understood that the calamities and hardships in this world are an expiation for sins, but all of this occurs under Allah’s will. Therefore, a person should supplicate to Allah with utmost humility for His grace and mercy.
All matters are in His hands; He disposes of them according to His will and decree. All humans are in need of Him and are His servants.
Despite this, Allah does not wrong anyone.
And Allah knows best.

Relevance Between the Chapter and the Hadith
The Chapter of Sahih Bukhari: «بَابُ عَلاَمَاتِ النُّبُوَّةِ فِي الإِسْلاَمِ:»
Imam Bukhari rahimahullah, in the chapter heading (tarjamat al-bab), alluded to the signs of prophethood and shed light on the evidences of prophethood. However, the hadith he presented apparently does not contain any explicit sign of prophethood that would connect the hadith to the chapter heading. While establishing the relevance between the chapter heading and the hadith, Hafiz Ibn Hajar rahimahullah states:
«وجه دخوله فى هذا الباب : اٴن فى بعض طرقة زيادة تقتضي ايراده فى علامات النبوة، وهى قوله صلى الله عليه وسلم ”اما اذا أبيت فهي كما تقول، قضاء (الله) كائن فما أمسي من الغد ألا ميتا“ وبهذه الزيادة يظهر دخول هذا الحديث فى هذا الباب .» [فتح الباري لابن حجر : 521/7]
That is, the relevance of the chapter heading to the hadith is such that in its other chains (turq), there is a sign of the signs of prophethood. (Some of its chains), as narrated by Tabarani, are reported from Ibn Abbas radi Allahu anhuma, whose final words are as follows: «فما أمسي من الغد الا ميتا» “So he died the next day.” Thus, it happened exactly as the Prophet of Allah sallallahu alayhi wa sallam had said, and from here the connection between the chapter heading and the hadith is established.

Allamah Ayni rahimahullah stated:
«مطابقة للترجمة تؤخذ من قوله : ”فنعم اذا“ فذالك من حيث ان الاعرابي لما رد على النبى صلى الله عليه وسلم قوله : ”لا بأس طهور ان شاءالله“ مات على وفق ما قاله صلى الله عليه وسلم، وهذا معجزاته صلى الله عليه وسلم .» [عمدة القاري للعيني : 149/16]
The correspondence between the chapter heading and the hadith will be taken from these words: “Well then, so it shall be,” when the Prophet sallallahu alayhi wa sallam said to the Bedouin, «لا باس طهور انشاءالله» and when the Bedouin rejected this statement of the Prophet sallallahu alayhi wa sallam, then he died exactly as the Prophet sallallahu alayhi wa sallam had said, and this was a miracle of the Prophet sallallahu alayhi wa sallam (the prophecy of his death).

According to Allamah Ayni rahimahullah, the relevance between the chapter and the hadith is due to the prophecy of the Prophet sallallahu alayhi wa sallam, because making prophecies is a miracle of a prophet, and in the chapter heading as well, Imam Bukhari rahimahullah has indicated this very matter.

Hadith Commentary:
That is, you will die from this illness. Imam Bukhari rahimahullah has cited this hadith here to indicate towards its other transmission, which has been narrated by Tabarani. In that narration, it is stated that he died the next day. Just as you (sallallahu alayhi wa sallam) had said, so it happened.

Hadith Commentary:
➊
This Bedouin, rejecting the statement of the Messenger of Allah (sallallahu alayhi wa sallam), said:
“This fever will carry him to the grave.”
The Messenger of Allah (sallallahu alayhi wa sallam) said:
“Yes, now it will be as you say.” Thus, in accordance with his statement, he died from that very fever.
Imam al-Bukhari (rahimahullah) has alluded to another narration from this hadith, that the Bedouin died the next day, just as the Messenger of Allah (sallallahu alayhi wa sallam) had said.
(al-Mu‘jam al-Kabir by al-Tabarani: 7/306)
➋
This is a miracle of the Messenger of Allah (sallallahu alayhi wa sallam) and a proof of his prophethood, that what he said came to pass exactly as stated.
➌
The name of this Bedouin was Qays.
And Allah knows best.