Bukhari

Hadith Commentary:
The purpose here is to express the simplicity and ease of the Shariah, which it has placed at the forefront in matters of teaching, learning, issuing legal verdicts (fatwa), and guidance.
In some narrations, it is mentioned that the Prophet (sallallahu alayhi wa sallam) was not on his mount at that time, but rather was seated and explaining issues to the people.
Therefore, the reconciliation is that at some point, the Prophet (sallallahu alayhi wa sallam) explained issues while seated on his mount, and later he dismounted and sat down.
Each narrator described the state in which he saw the Prophet (sallallahu alayhi wa sallam).

Hadith Commentary:
(1)
Imam Bukhari rahimahullah has previously established two similar chapter headings for this hadith narrated from Abdullah bin Amr bin al-As radi Allahu anhu, the wording of which is as follows:
• Answering questions while seated on a riding animal.
• Question and answer during the stoning of the Jamarat.
Apparently, this seems like repetition, but such instances are rare and uncommon.
(Fath al-Bari: 3/718)
And Allah knows best.

(2)
It should be noted that in these ahadith, the meaning of "waqafa" is not to stand, but rather to stop or pause while seated on the riding animal.
In this hadith of Abdullah bin Amr radi Allahu anhu, the precedence and delay regarding four matters have been mentioned:
• Shaving the head before slaughtering the sacrificial animal.
• Shaving the head before stoning.
• Slaughtering before stoning.
• Performing the Tawaf al-Ifadah before stoning.
In the hadith narrated from Ali radi Allahu anhu, performing Tawaf al-Ifadah before shaving the head is mentioned, while in the hadith narrated from Jabir radi Allahu anhu, performing Tawaf al-Ifadah before slaughtering is mentioned.
It is narrated from Usamah radi Allahu anhu that the Messenger of Allah sallallahu alayhi wa sallam was asked about performing Sa’i before Tawaf.
(Sunan Abi Dawud, Manasik, Hadith: 2015)
In any case, if any act is done out of forgetfulness or ignorance in a different order, then no expiatory sacrifice (dam) is obligatory in it.

(3)
Imam Muslim has mentioned the corroboration (mutaba’ah) of Ma’mar bin Rashid with these words: I saw the Messenger of Allah sallallahu alayhi wa sallam in Mina, mounted on his camel, when a man came to him...
(Sahih Muslim, Hajj, Hadith: 3162(1306))

(4)
The purpose of Imam Bukhari rahimahullah is to highlight the simplicity and ease of the Shari’ah, which it has maintained in the matters of teaching, learning, invitation (da’wah), and issuing legal verdicts (fatwa).
In some narrations, it is mentioned that the Messenger of Allah sallallahu alayhi wa sallam was seated at that time and was informing the people about religious matters.
This means that he was explaining issues while seated on his riding animal.
(Fath al-Bari: 3/719)