Bukhari

Hadith Commentary:
Because the Prophet (sallallahu alayhi wa sallam) arrived in Makkah on the 4th of Dhul-Hijjah and returned to Madinah on the 14th, the total duration of stay was ten days, and he stayed in Makkah itself for only four days; the remaining days were spent in Mina and elsewhere. For this reason, Imam Shafi’i (rahimahullah) said that when a traveler intends to stay at a place for more than four days, he should perform the full prayer; up to four days, he should continue to shorten (qasr) the prayer. Imam Ahmad (rahimahullah) said: up to twenty-one prayers (i.e., the number of obligatory prayers in that period) (Maulana Waheed uz-Zaman, may Allah have mercy on him).

The previous narration, in which the Prophet’s (sallallahu alayhi wa sallam) stay is mentioned as twenty-one days, refers to his stay at the time of the conquest of Makkah.

Hafiz Ibn Hajar (rahimahullah) states that Imam Bukhari (rahimahullah) has, in the Book of Maghazi, mentioned through another chain that the place of stay was Makkah, where the Prophet (sallallahu alayhi wa sallam) stayed for nineteen days and continued to shorten the prayer. It is thus understood that this is the maximum limit for qasr; if one decides to stay longer than this, he must perform the full prayer. However, if he is unable to decide and remains in a state of hesitation, saying “today or tomorrow” (i.e., undecided about departure), then as long as he is in this state, he may continue to shorten the prayer. As Allamah Ibn Qayyim (rahimahullah) has stated in Zad al-Ma’ad:

“And among them is that the Messenger of Allah (sallallahu alayhi wa sallam) stayed in Tabuk for twenty days, shortening the prayer, and he did not say to the ummah that if anyone among them stays somewhere (in the state of travel) for longer than that, he should not shorten the prayer. He never said such a thing. Therefore, when a person, while traveling, does not stay at a place as a resident nor intends to settle there, but remains in a state of hesitation about his stay, whether it is short or long, he remains under the ruling of a traveler and may shorten the prayer.”

Hafiz (Ibn Hajar) said that some people have misunderstood Ahmad to mean Imam Ahmad ibn Hanbal; this is completely incorrect, because Imam Ahmad did not hear from Abdullah ibn Mubarak (Wahidi).

Hadith Commentary:
In this hadith, the arrival of the Messenger of Allah (sallallahu alayhi wa sallam) in Makkah Mukarramah is mentioned; the departure towards Mina is not described because there is no need for clarification regarding that.
The purpose here is to describe the duration of stay which the Messenger of Allah (sallallahu alayhi wa sallam) adopted during the Farewell Pilgrimage (Hajjat al-Wada‘) with complete determination and certainty, and that is: excluding the day of arrival and the day of departure, three days and three nights, such that he arrived in Makkah on the 4th of Dhu al-Hijjah and departed for Mina on the 8th of Dhu al-Hijjah.
And in this way, he performed a total of twenty prayers in the state of residence in Masjid al-Haram.
It has also been said that what is meant is the period between arrival in Makkah and departure for Madinah Munawwarah, as is mentioned in the hadith narrated from Anas (radi Allahu anhu) that he (sallallahu alayhi wa sallam) stayed for ten days, meaning arrival on the 4th of Dhu al-Hijjah and departure for Madinah on the 14th of Dhu al-Hijjah.
(Fath al-Bari: 2/730)
Imam al-Bukhari (rahimahullah) has narrated the corroboration of ‘Ata’ with a connected chain.
(Sahih al-Bukhari, Book of Hajj, Hadith: 1568)