Bukhari

Hadith Commentary:
➊
From this hadith, it is understood that people's conditions and dealings should be judged according to what is apparent. Therefore, whoever manifests the symbols of the religion, the rulings of the Muslims will be applied to him, as long as nothing contrary to the religion becomes apparent from him.
And the mention of facing the qiblah and eating slaughtered meat, etc., is because some among the People of the Book, even though they profess monotheism and face the qiblah, do not perform prayers like ours, nor do they use our qiblah, and many among them slaughter for other than Allah, and many do not eat our slaughtered meat. Also, a person's prayer and food become known very quickly, even on the very first day, whereas other religious matters are not known so quickly. For this reason, only a few things have been mentioned.
(Fath al-Bari: 1/644)
From this, it is understood that those who do not pray like us or do not eat our slaughtered meat have themselves become separated from us and have begun to consider their religion as distinct from ours. Thus, before our judgment, it is as if they have already passed judgment upon themselves.
➋
The signs mentioned in the hadith are major and clear signs of the people of Islam, by which they are easily distinguished from the followers of other religions.
It is as if these signs have become emblems for the people of Islam. However, this does not mean that whoever possesses these three things must necessarily be considered a Muslim, even if he denies the essentials of the religion and, according to the statement of the Messenger of Allah (sallallahu alayhi wa sallam), exits the religion of Islam just as an arrow leaves the bow.
It is evident that if a person accepts the entire religion and acts upon it, but denies even a small surah of the Qur'an, or does not accept its ruling, or deliberately interprets it incorrectly, there can be no doubt about his disbelief. How much more so if a person claims prophethood, adopts the practice of insulting the Prophets (alayhim as-salam), uses extremely inappropriate words against their status, distorts the religion, denies or mocks the hadiths, reports, events, and miracles—how can such a person be considered within Islam? Indeed, Mirza Ghulam Ahmad Qadiani committed all these acts of disbelief, whereas committing even one of them would have been sufficient to establish disbelief. Therefore, this person, despite professing the kalimah, is outside the religion of Islam and is an apostate.
There is no need for hesitation or caution regarding his disbelief, because just as being hasty in declaring a Muslim to be a disbeliever (takfir al-Muslim) is a sin, likewise, refraining from declaring a disbeliever to be a disbeliever (not performing takfir of a kafir) is also a sin.
Note:
In light of this hadith, the ruling regarding Jews, Christians, Magians, and polytheists is clear. However, regarding the false sects that have arisen within the Muslims, the judgment of faith and disbelief requires much deliberation.
A detailed discussion on this will be presented later under the book "Istitabah al-Murtaddin," Hadith: 6924, inshaAllah ta'ala.