Bukhari

Hadith Commentary:
The aforementioned ahadith have already been mentioned earlier in the Book of the Appointed Times (Kitab al-Mawaqit).
The purpose of mentioning these ahadith here is to clarify that Hell (Jahannam) already exists and its fire is burning, and due to its raging and boiling, the heat in this world increases, as will be further explained in the upcoming hadith.

Hadith Commentary:
(1)
The command to perform the prayer after cooling (abrad) apparently contradicts the following hadith:
Hazrat Khabbab bin Aratt (radi Allahu anhu) narrates that we complained to the Messenger of Allah (sallallahu alayhi wa sallam) about praying on hot sand, so he alleviated our complaint.
(Sahih Muslim, Al-Masajid, Hadith: 1406(619))

This contradiction can be resolved in the following ways:
➊ In the narration of Hazrat Khabbab bin Aratt (radi Allahu anhu), the request that was made was for a delay even greater than abrad, meaning the demand was to delay until the heat of the ground had completely dissipated. Accepting this request carried the risk that the time for the prayer might lapse, so the request was not granted. However, it is recommended (mustahabb) to delay until the intensity of the heat subsides.
➋ The hadith of Hazrat Khabbab bin Aratt (radi Allahu anhu) can be considered abrogated (mansukh) by the ahadith of abrad. This is supported by a narration from Hazrat Mughirah bin Shu’bah (radi Allahu anhu), who says:
“We used to pray with the Messenger of Allah (sallallahu alayhi wa sallam) at the peak of midday, then he commanded that the Zuhr prayer be performed at a cooler time.”
(Sunan Abi Dawud, As-Salat, Hadith: 680)

It is narrated from Imam Ahmad (rahimahullah) that performing the prayer after cooling during intense heat was the final decision of the Messenger of Allah (sallallahu alayhi wa sallam).
(Fath al-Bari: 2/23)

Therefore, it is recommended (mustahabb) to delay the Zuhr prayer somewhat during intense heat.

(2)
After narrating this report, Imam Bukhari (rahimahullah) has also mentioned several corroborating narrations (mutaba‘at) in support of it, showing that Hafs bin Ghiyath is not alone in narrating from A‘mash regarding performing Zuhr prayer after cooling during intense heat. Rather, Sufyan Thawri, Yahya bin Sa‘id al-Qattan, and Abu ‘Awanah have also narrated these words from A‘mash, and these corroborations with connected chains are present in the books of hadith.
(Fath al-Bari: 2/27)

(3)
Imam Bukhari (rahimahullah) has maintained excellent order in presenting the ahadith under this chapter, which is evidence of his deep understanding and mature insight. In the first hadith, abrad is mentioned in an absolute sense. The second hadith provides guidance regarding this abrad, indicating that it is permissible until the shadows of the mounds appear. The next hadith explains the reason due to which the absolute (mutlaq) is interpreted in light of the restricted (muqayyad). In the final hadith, the restriction is clarified, specifying that what is meant is the Zuhr prayer.
(Fath al-Bari: 2/27)