Bukhari

Hadith Commentary:
You were aware that the Ansar would not receive the caliphate; therefore, you instructed that good treatment be shown towards them.
The relevance of this hadith to the chapter is evident.

Hadith Commentary:
➊
In this hadith, there is information about the unseen: that people will be many, but the number of the Ansar will continue to decrease as before, because the Ansar are those who gave shelter to the Prophet (sallallahu alayhi wa sallam) and the noble Companions (radi Allahu anhum).
They nurtured the religion of Islam in times of hardship and difficulty.
Such a time will not come again.
On this basis, the number of non-Ansar increased and their (the Ansar's) numbers decreased; thus, from the tribes of Aws and Khazraj, very few descendants continued. Although many people claim to be from the Ansar, mere claims of abundance have no validity.
It should be understood in its real sense, because the offspring of the Muhajirun spread into the cities and they also became rulers and owners of kingdoms, but the Ansar did not attain such abundance.

➋
In this, there is also an indication that the Ansar will not receive the caliphate, and for this reason, the Prophet (sallallahu alayhi wa sallam) advised good treatment towards them.
In any case, the prophecy of the Messenger of Allah (sallallahu alayhi wa sallam) was fulfilled: the Ansar are as few in number as salt in food.
And Allah knows best.

Hadith Commentary:
This was your last sermon in Masjid Nabawi.
According to your prophecy, the Ansar are now found only in small numbers in the world.
The lineages of other Arab elders have spread throughout the entire Islamic world.
One should be sacrificed for this noble generosity.
In return for the favor that the Ansar helped you and Islam in times of poverty and hardship, you (sallallahu alayhi wa sallam) are instructing your entire Ummah to consider the Ansar as their benefactors.
Deal with those among them who are good with even greater kindness, and pardon those who are bad, for their forefathers helped Islam in a time of great destitution.
All the hadiths that have been mentioned in this chapter are cited here only because the phrase "Amma ba'd" is mentioned on the occasion of some sermon, etc.
Qastallani (rahimahullah) said that the meaning of the hadith is not that the legal punishments (hudud) are lifted from the Ansar; rather, the Prophet (sallallahu alayhi wa sallam) emphasized the establishment of hudud upon everyone, rich or poor.
Here, minor mistakes of the Ansar are meant, that they should be overlooked.
Imam al-A'immah, Imam Bukhari (rahimahullah), has narrated various hadiths under this chapter.
In all of them, the chapter heading is derived from the phrase "Amma ba'd."
The Prophet (sallallahu alayhi wa sallam) used to employ the phrase "Amma ba'd" after praising Allah in every sermon.
In the previous connected hadith, there is mention of your (sallallahu alayhi wa sallam) public address after 'Isha, in which you used the phrase "Amma ba'd."
You had sent Ibn Lubbaytah to collect zakat; when he returned with the zakat wealth, he began to say about some items that these were given to him as gifts. At that time, you delivered this admonition after 'Isha and expressed strong displeasure, saying: If a person goes on an official mission to collect zakat, what right does he have to accept gifts for himself during that journey, when whatever he receives is the right of the Islamic treasury (Bayt al-Mal)?
Imam Bukhari (rahimahullah) has transmitted this hadith in full in the chapters of Faith and Vows.
In the previous hadith, there is mention of one of the last and absolutely final public addresses of the Prophet (sallallahu alayhi wa sallam), which he delivered in his illness before death, and in which, after praising Allah, he used the phrase "Amma ba'd."
Then he made a bequest regarding the Ansar, that in the future it will be the duty of Muslims in authority to pay special attention to the rights of the Ansar.
They should look upon the good among them with respect and overlook the faults of the bad among them.
Indeed, the Ansar possess a unique history within the Muslim Ummah until the Day of Judgment, which can be called the golden era of Islam.
This is, in fact, the history of the Ansar; therefore, honoring and respecting the Ansar is a religious duty upon every Muslim.

Hadith Commentary:
(1)
There is no doubt that the Ansar of Madinah have written a golden chapter in the history of Islam with regard to their religious services. They are great benefactors of the Muslim Ummah; therefore, honoring and respecting them is a religious obligation upon every Muslim. The Messenger of Allah (sallallahu alayhi wa sallam) said:
“The number of the Ansar will continue to decrease day by day until they remain only as much as the salt in food.” (Hadith: 3628)

(2)
In this hadith, the phrase "Amma ba'd" was used; for this reason, Imam Bukhari (rahimahullah) has mentioned it. Its complete details will be explained in the chapter on the Virtues of the Ansar.

(3)
Hafiz Ibn Hajar (rahimahullah) has mentioned, in addition to the aforementioned ahadith, a few other ahadith in which the phrase "Amma ba'd" is used, and he has stated that Hafiz Abdul Qadir Rahawi (rahimahullah) has compiled the ahadith in which the phrase "Amma ba'd" is used. Approximately 32 Companions (radi Allahu anhum) have narrated such ahadith. Among them is a hadith narrated from Hazrat Miswar bin Makhramah (radi Allahu anhu) that whenever the Messenger of Allah (sallallahu alayhi wa sallam) delivered a sermon, he would say "Amma ba'd" in it. Its narrators are trustworthy. The wording of this hadith indicates that the Messenger of Allah (sallallahu alayhi wa sallam) would always perform this act. (Fath al-Bari: 2/521)