Bukhari

Hadith Commentary:
In the two scenarios mentioned at the beginning of the chapter, the seller no longer retains the option to annul the sale, because he did not object to the buyer’s act of disposal, but rather remained silent. In the hadith of the chapter, only the mention of a gift (hibah) is found, but manumission (i‘taq) is analogized to a gift, as both are forms of voluntary transfer (tabarru‘).
The purpose of Imam Bukhari rahimahullah in bringing this chapter is to show that the hadith of the chapter does not negate the option of the session (khiyar al-majlis).
This has already been established above from the hadith of Ibn ‘Umar radi Allahu anhu, because this option lapses due to the buyer’s act of disposal and the seller’s silence; thus, his silence nullifies the option.
Ibn Battal said: Those who say that a sale is not complete without physical separation (tafarraq al-abdan) do not permit the buyer to dispose of the item before separation.
And this hadith is an argument against them.
As for selling before taking possession (qabd), according to Imam Shafi‘i rahimahullah and Muhammad rahimahullah, it is absolutely not permissible. According to Imam Abu Hanifah rahimahullah and Abu Yusuf rahimahullah, the sale of movable property before possession is permissible, but not that of immovable property.
And our Imam Ahmad ibn Hanbal rahimahullah, al-Awza‘i, and the Ahl al-Hadith hold that it is not permissible to sell items measured by weight or volume before taking possession, but it is permissible for other items.
Qastallani said: The hadith of ‘Umar radi Allahu anhu does not contradict those authentic hadiths which establish the option of the session (khiyar al-majlis), because it is possible that after the contract of sale, the Prophet sallallahu alayhi wa sallam moved slightly ahead or behind ‘Umar radi Allahu anhu for a short while, and then made the gift.
And Allah knows best (Wahidi).
The Prophet sallallahu alayhi wa sallam, after taking the camel from ‘Umar radi Allahu anhu, immediately gifted it to his son ‘Abdullah radi Allahu anhu, and ‘Umar radi Allahu anhu did not object to this, so the sale was valid and the option of the session no longer remained.
At the end of the chapter, there is mention of a transaction between ‘Abdullah ibn ‘Umar radi Allahu anhu and ‘Uthman radi Allahu anhu, in which the mentioned Wadi al-Qura is a settlement near Tabuk, about six or seven stages from Madinah. In the time of the people of Thamud, this place was inhabited. Qastallani said: The relevance of the mentioned incident to the chapter is that it is permissible for the seller and buyer to separate by their own will or to annul the sale.

Hadith Commentary:
(1)
The valley in which Ibn Umar radi Allahu anhu owned land was called Wadi al-Qura, which is located six or seven stages from Madinah Tayyibah, near Tabuk, and the people of Thamud used to inhabit that very place.

(2)
Imam Bukhari rahimahullah has established the ruling of "khiyar al-majlis" (the option of cancellation while both parties are still present at the place of contract) from this hadith.
The incident involving Umar radi Allahu anhu and the unruly camel was an obstacle to establishing khiyar al-majlis, so Imam Bukhari rahimahullah added some words in the chapter heading to address this.
There, khiyar al-majlis was forfeited because the buyer made use of the item in the presence of the seller, and his silence (remaining quiet) nullified the khiyar al-majlis.

(3)
Some people think that the practice of "tafarraq bi al-abdan" (physical separation to end the option) had been abandoned before the time of Ibn Umar radi Allahu anhu, but this view is contrary to the apparent wording of the hadith. Furthermore, the wording of the narration from Ayyub ibn Suwayd is as follows:
Whenever we engaged in buying and selling, both the seller and the buyer retained the option until they separated from each other. Accordingly, I made a transaction with Uthman radi Allahu anhu, and then he narrated this incident.
This means that this practice was still in effect at the time of transacting with Uthman radi Allahu anhu.
(Fath al-Bari: 4/424)