Bukhari

Hadith Commentary:
This is the sermon of the Day of Arafah, and the sermon of Mina is the subsequent one, which was delivered on the tenth (of Dhul-Hijjah). In that, there is a clear explanation of the Day of Sacrifice (Yawm al-Nahr).
So, this hadith which appears in the Sahih states that he (sallallahu alayhi wa sallam) delivered this sermon on the Day of Sacrifice, and it is established that he delivered this same sermon before that on the Day of Arafah.
(Fath al-Bari)
That is, it is clearly mentioned in the hadith of Sahih al-Bukhari that the Prophet (sallallahu alayhi wa sallam) delivered the sermon on the Day of Sacrifice (Yawm al-Nahr), and it is also established that before this, he (sallallahu alayhi wa sallam) delivered this same sermon on the Day of Arafah as well.

Hadith Commentary:
(1)
Generally, there are six days of Hajj, which begin from the 8th of Dhul-Hijjah and continue until the 13th of Dhul-Hijjah.
The first day is called Yawm at-Tarwiyah, the second Yawm Arafah, the third Yawm an-Nahr, the fourth Yawm al-Qar, the fifth Yawm an-Nafr al-Awwal, and the sixth Yawm an-Nafr ath-Thani.
(2)
During these days, in accordance with the occasion and place, the Imam should make arrangements to deliver a sermon (khutbah) in order to admonish and advise the people.
The first sermon, which is delivered on the 9th of Dhul-Hijjah, is before the prayer, and the remaining three sermons are after it.
Among these, one sermon is on the day of sacrifice (Yawm an-Nahr).
Some people deny that the sermon on this day is Sunnah.
According to them, these are admonitions (wasaya) which the Prophet (sallallahu alayhi wa sallam) instructed the Ummah with, and they do not contain rulings and issues related to Hajj.
Imam al-Bukhari (rahimahullah) refuted them by establishing that, according to the narrator, this is a sermon (khutbah) just as a sermon was delivered on the day of Arafah.
On this basis, delivering a sermon on the day of sacrifice is also a Prophetic Sunnah; it is not merely a general admonition or instruction.
Since one of the objectives of Hajj is to call the Muslim world to unity and harmony, these sermons are the best means for this purpose. Therefore, the preacher should shed light on global issues along with the rulings of Hajj, call to adherence to the Book of Allah and the Sunnah of the Messenger of Allah, and also invite to mutual agreement and unity. This is the greatest objective of the Hajj to the House of Allah.
(3)
In another narration from Ibn Abbas (radi Allahu anhu), there is mention of delivering a sermon in the plain of Arafat.
Imam al-Bukhari (rahimahullah) cited this hadith to show that the narrator of the hadith of Ibn Abbas (radi Allahu anhu) refers to the admonition and instruction on the day of Arafah as a sermon (khutbah), and since there is no disagreement regarding the Sunnah status of the sermon on that day, then when the same narrator refers to the admonition and advice on the day of sacrifice as a sermon, what need is there to subject it to dispute?
In any case, delivering a sermon on the tenth (of Dhul-Hijjah) is also Sunnah.
(4)
At the end of the hadith, Imam al-Bukhari (rahimahullah) has also mentioned a corroborating narration (mutaba‘ah), which Imam Ahmad ibn Hanbal (rahimahullah) has narrated with a connected chain. Although in it, the place of the sermon is not specified.
(Fath al-Bari: 3/726)
And Allah knows best.