Bukhari

Hadith Commentary:
Allamah Ibn Hajar states:
“The Eid is not specified in this narration, and the implication of including this hadith under the chapter of fasting on the Day of Sacrifice is that the day being asked about is the Day of Sacrifice (Yawm al-Nahr), and this is explicitly stated in the narration of Yazid ibn Zuray‘ as mentioned, and its wording is: ‘It coincided with the Day of Sacrifice.’”
That is, in this narration, there is no clarification as to which Eid it was, and here, the context of the chapter implies Eid al-Adha. This is explicitly stated in the narration of Yazid ibn Zuray‘, in which it is mentioned that, by coincidence, that day happened to be the day of sacrifice.
This wording is present with clarity in the narration of Yazid ibn Zuray‘.
And likewise, it is found in the narration of Ahmad, which he transmitted from Isma‘il ibn ‘Ulayyah, who narrated from Yunus. Thus, it is established that what is meant by “the day of Eid” in the narration is Eid al-Adha, the Day of Sacrifice (Yawm al-Nahr).

Hadith Commentary:
(1)
Hafiz Ibn Hajar rahimahullah writes:
There is no clarification in this narration as to which Eid it was, but the title necessitates that what is meant is the day of Eid al-Adha. Thus, in the narration of Yazid bin Zuray’, this is explicitly stated, meaning that the day on which the vow to fast was made happened to coincide with the day of Eid al-Adha.
Ibn Umar radi Allahu anhu, in view of the apparent conflict of evidences, refrained from giving a clear answer.

(2)
Allamah Khattabi rahimahullah says:
There is a difference of opinion in this matter.
Some have said:
If someone vowed that he would fast on the day so-and-so arrives, and that person arrived on the day of Eid, then he should neither fast nor make up (qada) for it.
Some have said that he should not fast on the day of Eid, but should make up (qada) for it later.
Some scholars are of the opinion that where both a command and a prohibition are combined, the prohibition should be acted upon; therefore, the fast should not be observed on that day, nor is it necessary to make it up.
(Fath al-Bari: 4/306)
According to us, the preferred position is that the prohibition should be given precedence, and the fast should not be observed on that day, just as the Messenger of Allah sallallahu alayhi wa sallam commanded the person who had vowed to perform Hajj on foot to ride (i.e., use a mount).
If it had been necessary to fulfill the vow in such circumstances, he would not have commanded him to use a mount.
In the present case as well, it is not necessary to fulfill the vow, because fasting on that day is not permissible; therefore, he will not fulfill his vow in any way.
(Fath al-Bari: 4/307)

Hadith Commentary:
The best evidence has been presented that for true Muslims, there can be no greater proof than the example of the Prophet (sallallahu alayhi wa sallam).

Hadith Commentary:
(1)
The scholars are unanimous that it is not permissible to observe a voluntary, obligatory, or vowed fast on the days of Eid al-Fitr and Eid al-Adha. It is narrated from Abu Sa'id al-Khudri radi Allahu anhu that the Messenger of Allah sallallahu alayhi wa sallam forbade fasting on the days of Eid al-Fitr and Eid al-Adha.
(Sahih al-Bukhari, al-Sawm, Hadith: 1991)
If a person vows to fast for a certain number of days and Eid al-Fitr or Eid al-Adha falls within those days, then Imam al-Shafi'i rahimahullah says that he should neither fast on those days nor is it necessary to make up the missed fasts. However, Imam Abu Hanifah rahimahullah says that he should not fast on those days, but it is necessary to make up the missed fasts.

(2)
Hafiz Ibn Hajar rahimahullah, at the end of the first hadith, has transmitted an addition from Allamah Isma'ili, that when this matter was mentioned to Hasan al-Basri rahimahullah, he said that instead, a fast should be observed on another day later.
(Fath al-Bari: 11/720)
And Allah knows best.

Hadith Commentary:
Benefits and Issues:
According to unanimous agreement among the Ummah, it is forbidden (haram) to fast on the days of Eid al-Fitr and Eid al-Adha. However, if someone makes a vow (nadhar) to fast on these days, then according to the majority of the Imams, such a vow will be null and void. According to Imam Abu Hanifah rahimahullah, the vow will be considered binding and its fulfillment (qada) will be necessary. If someone actually fasts on that day, the fast will be valid. That is, if someone vows to fast on a specific date, or to fast on a Monday or Thursday in the first week of a certain month, and that day coincidentally turns out to be an Eid day, then according to the majority, the vow to fast will be null and void. However, according to Imam Abu Hanifah rahimahullah, fulfillment (qada) of the vow is necessary because the vow has become binding.