Bukhari

Hadith Commentary:
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The purpose of Imam Bukhari rahimahullah is to show that just as in the absence of water, one may perform tayammum in place of ablution (wudu) and ritual bath (ghusl), similarly, if there is only enough water to quench thirst, then in such circumstances, tayammum may also be performed. And if there is more water, sufficient for ablution or ritual bath, but its use poses a risk of illness or death, then there is also no harm in performing tayammum.
In this regard, he has presented two narrations. The first narration is brief and contains some advancement and delay (in the order of events). Imam Bukhari rahimahullah has therefore mentioned the second narration so that the actual situation of the debate between Abu Musa al-Ash‘ari radi Allahu anhu and Abdullah ibn Mas‘ud radi Allahu anhu becomes clear. Abdullah ibn Mas‘ud radi Allahu anhu did not permit tayammum for one in a state of major ritual impurity (junub).
Upon this, Abu Musa al-Ash‘ari radi Allahu anhu first presented the incident of ‘Ammar and ‘Umar radi Allahu anhuma. Abdullah ibn Mas‘ud radi Allahu anhu, following the principles of debate, replied that ‘Umar radi Allahu anhu had said to ‘Ammar radi Allahu anhu, “Fear Allah regarding this matter.”
The meaning was that the very incident you are presenting as evidence is denied by the person involved himself, so how can it be presented as proof in such circumstances? After this, Abu Musa radi Allahu anhu presented the verse of tayammum as evidence, to which Abdullah ibn Mas‘ud radi Allahu anhu could not respond. Rather, he was compelled to reveal the real underlying reason, that his objection was due to a legal expediency (maslahah shar‘iyyah): that under the pretext of this permissibility, everyone would begin to perform tayammum even in slight cold, which is not the intent of the Shari‘ah.
In view of this expediency, he did not wish to issue this legal verdict (fatwa).
Hafiz Ibn Hajar rahimahullah says that Abdullah ibn Mas‘ud radi Allahu anhu had retracted his fatwa regarding tayammum for one in a state of major ritual impurity (junub), as is found in the Musannaf of Ibn Abi Shaybah, but there is a break in its chain of transmission.
(Fath al-Bari: 1/593)
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The verse of tayammum which Abu Musa al-Ash‘ari radi Allahu anhu presented as evidence contains the words: “aw lamastum al-nisa’” (or you have touched women). If by this, intercourse (jima‘) was not meant, then Abdullah ibn Mas‘ud radi Allahu anhu could have replied that the verse you are presenting as evidence, in it, “touch” does not mean intercourse, but rather physical touch by hand is meant, i.e., here the matter is not about major ritual impurity (janabah), but about minor impurity (hadath asghar). However, Abdullah ibn Mas‘ud radi Allahu anhu did not say this. From this, it is understood that according to him as well, in this noble verse, “touch” does not mean touch by hand, but rather intercourse.
(I‘lam al-Hadith by al-Khattabi: 1/345)