Bukhari

Hadith Commentary:
That is, obedience to even the lowest authority is necessary, provided that they do not command disobedience to Allah.

Hadith Commentary:
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Obedience to even the lowest of leaders is obligatory, provided that he does not command disobedience or sin.
The Arabs were unfamiliar with the system of leadership, so the Messenger of Allah (sallallahu alayhi wa sallam) encouraged them to obey and follow their leaders, so that in both times of peace and war they would remain subject to their leaders and not spread chaos, thereby tearing apart the unity of Islam.
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The Messenger of Allah (sallallahu alayhi wa sallam) likened the head of an Abyssinian to a dried grape; by this is meant an exaggeration in expressing contempt or dislike, i.e., even if such a person is appointed, obedience to him is also necessary.
This does not refer to the caliphate, because the caliphate is the exclusive right of the Quraysh, provided that they are determined to uphold the religion and are in a position to practically implement the limits set by Allah.

Hadith Commentary:
From this, the purpose of the chapter is derived as follows: when obedience to an Abyssinian (Habashi) slave who is a ruler has been commanded, then his leadership (imamah) in prayer is, a fortiori, valid—because in that era, whoever was the ruler would also lead the prayer as imam.

From this hadith, it is also deduced that fighting and causing disorder against the ruler of the time—even if he is unjust or foolish—is not permissible, provided that he is a legitimate caliph, i.e., appointed as king on behalf of the Quraysh.

This does not mean that the caliphate of an Abyssinian slave is valid, because the caliphate is not valid for any nation other than the Quraysh, as is established from another hadith (Maulana Waheed al-Zaman, rahimahullah).

Hadith Commentary:
In the narration, "Habashi" refers to an Abyssinian slave, as clarified in another narration.
(Sahih al-Bukhari, Al-Ahkam, Hadith: 7142)
The relevance of this hadith to the chapter is that when such a slave becomes a leader or governor, obedience to him is obligatory, and it is the practice of Islam that the leader and caliph are placed ahead of the congregation.
It can also be said that the command to obey him includes the command to pray behind him.
(Sharh al-Kirmani: 72/5)
In one narration, the Messenger of Allah (sallallahu alayhi wa sallam) said on the occasion of the Farewell Pilgrimage (Hajjat al-Wada’): If your ruler is an Abyssinian slave who leads you according to the Book of Allah, you must listen to him and obey him.
From this narration, the historical context of the Prophetic hadith and the direction of obedience become clear: that you (sallallahu alayhi wa sallam) gave this command on the occasion of the Farewell Pilgrimage and conditioned it upon leadership according to the Book of Allah.
(Fath al-Bari: 242/2)

Hadith Commentary:
(1)
Imam Bukhari rahimahullah has used this hadith as evidence for his chapter heading because such characteristics are generally found in a non-Arab ruler who has recently embraced Islam and does not yet have complete knowledge about the religion. For such a person, it is not unlikely to commit innovations (bid‘ah). Such rulers are often afflicted with self-admiration and self-deception. When obedience to such a ruler is necessary, then following him in prayer should also be valid. If such a ruler is worthy of obedience, then prayer led by him is also valid. (Fath al-Bari: 2/246)

(2)
Hafiz Ibn Hajar rahimahullah has written regarding this hadith an incident of Abu Dharr radi Allahu anhu: Once he arrived at the place of Rabadhah when the congregation was being held and a slave was performing the duties of imam. During the prayer, it was said to him that Abu Dharr radi Allahu anhu has arrived. He began to move back, but Abu Dharr said: My beloved (sallallahu alayhi wa sallam) advised me to listen to my leader and obey him, even if he is an Abyssinian slave with a severed nose. (Fath al-Bari: 2/242)

(3)
It should be clear that if an innovation (bid‘ah) reaches the level of disbelief (kufr) or polytheism (shirk), then its ruling is the same as shirk; just as it is not permissible to follow a polytheist in prayer, likewise a person who holds an innovation that constitutes disbelief (bid‘ah mukaffirah) is also not eligible for imamate. If he does not hold a bid‘ah mukaffirah, then in case of necessity, it is permissible to pray behind him. Its ruling is like that of a sinner (fasiq), and prayer behind him is valid; however, a person of innovation (bid‘ati) and one who causes discord (fitnah) should not be appointed as a permanent imam. And Allah knows best.