Bukhari

Hadith Commentary:
Hafiz Ibn Hajar rahimahullah states:
“Ayyam al-Tashreeq are the days after the Day of Sacrifice (Yawm al-Nahr), and there is a difference of opinion regarding whether they are two or three days. They are called Ayyam al-Tashreeq because the meat of the sacrifices is dried in the sun during these days, i.e., the meat is spread out in the sun to dry.” That is, Ayyam al-Tashreeq refers to the days after the Day of Sacrifice, the 10th of Dhu al-Hijjah, which are either two or three days—there is a difference of opinion on this (but the view that they are three is preferred).
And they are named Ayyam al-Tashreeq because during these days, the meat of the sacrifices would be spread out in the sun to dry.

“And what is preferred according to al-Bukhari is its permissibility for the mutamatti‘ (the one performing tamattu‘ Hajj), for he mentioned in the chapter the hadith of Aisha radi Allahu anha and Ibn Umar radi Allahu anhu regarding its permissibility and did not mention any other hadith.” That is, according to Imam al-Bukhari rahimahullah, it is permissible for the one performing tamattu‘ Hajj (who is unable to offer a sacrifice) to fast during these days. He has mentioned in the chapter the hadiths of Aisha radi Allahu anha and Ibn Umar radi Allahu anhu, and has not brought any other hadith besides these.

The hadiths in which prohibition is mentioned can be considered to apply to those who are not performing tamattu‘.
And the hadiths permitting it apply to the mutamatti‘ who does not have the means to offer a sacrifice.
In this way, reconciliation is achieved between both types of hadiths.

Hafiz Ibn Hajar rahimahullah’s conclusion is:
“The opinion of permissibility is preferred, and to this al-Bukhari inclined.”
(Fath)
That is, Imam al-Bukhari rahimahullah holds the view of permissibility, and this view is preferred.

Hadith Commentary:
(1)
For the one performing Hajj al-Tamattu', if he does not find a sacrificial animal, there is no objection to fasting during the Days of Tashreeq. Apart from this, other individuals should not fast on these days because these are days specified for eating, drinking, and the remembrance of Allah. It is mentioned in the hadith that the Days of Tashreeq are days of eating and drinking.
(Musnad Ahmad: 75/5)
(2)
Aishah (radi Allahu anha) and Ibn Umar (radi Allahu anhuma) have derived the following from the verse:
﴿فَمَن لَّمْ يَجِدْ فَصِيَامُ ثَلَاثَةِ أَيَّامٍ فِي الْحَجِّ﴾ “So whoever does not find [a sacrificial animal]—then a fast of three days during Hajj.”
(al-Baqarah 2:196)
In the noble verse, the words (فِي الْحَجِّ) “during Hajj” are general, whether it is before the Day of Sacrifice (Yawm al-Nahr) or after it. On this basis, the Days of Tashreeq are included in them.
(Fath al-Bari: 4/309)