Bukhari

Hadith Commentary:
After the passing of the Prophet, various tribes around Madinah who had previously accepted Islam now thought that Islam had ended. Therefore, some of them became idolaters again. Some followed Musaylimah the Liar, such as the people of Yamamah, and some remained Muslims but began to deny the obligation of zakat (almsgiving), and started interpreting the Qur’an in such a way that the taking of zakat was exclusive to the Prophet (sallallahu alayhi wa sallam).
Because Allah said:
﴿خُذْ مِنْ أَمْوَالِهِمْ صَدَقَةً تُطَهِّرُهُمْ وَتُزَكِّيهِمْ بِهَا وَصَلِّ عَلَيْهِمْ إِنَّ صَلَاتَكَ سَكَنٌ﴾ (al-Tawbah: 103)
And that no one other than the Prophet could bring them comfort through supplication.
The meaning of “and his reckoning is with Allah” is that whether or not there is faith in his heart is not our concern; his questioning will be before Allah on the Day of Judgment, and in this world, whoever says with his tongue “la ilaha illallah” will be considered a believer, and we will not attack his wealth or life.
In the words of al-Siddiq (radi Allahu anhu), the meaning of “distinction between prayer and zakat” is that whoever declares prayer to be obligatory but denies the obligation of zakat, we will certainly wage jihad against him.
Later, Umar (radi Allahu anhu) also agreed with the opinion of Abu Bakr (radi Allahu anhu), and all the Companions became unanimous, and they waged jihad against those who refused to pay zakat.
This was the insight and wisdom of al-Siddiq al-Akbar (radi Allahu anhu).
If he had not acted with such resolve, the Islamic system would have been disrupted at that very moment, but al-Siddiq al-Akbar (radi Allahu anhu), with his firm determination, saved Islam from a great tribulation.
Even today, the Islamic law is that a person does not become a Muslim merely by uttering the kalimah unless he also acknowledges the obligation of prayer, zakat, fasting, and hajj, and, when the time comes, performs them.
Whoever denies the obligation of any pillar of Islam is, by consensus, outside of Islam and a disbeliever.
As for prayer, it is clearly stated: “Whoever deliberately abandons prayer has committed disbelief (kufr).” Whoever intentionally, without a valid excuse, abandons even one prayer has committed an act of disbelief.
For the denial of zakat, the fatwa of jihad by al-Siddiq al-Akbar (radi Allahu anhu) exists, and regarding hajj, the statement of al-Faruq al-Azam (radi Allahu anhu) is noteworthy, in which he requested a list from the Islamic state of those who are Muslims and upon whom hajj is obligatory but do not perform this obligation. He said that jizyah should be imposed upon them; they are excluded from the community of Muslims.

Hadith Commentary:
(1)
Upon the passing of the Messenger of Allah (sallallahu alayhi wa sallam), people were divided into three groups, the details of which are as follows:
✦ Some people apostatized from Islam and returned to disbelief, rejecting the laws of Islam, that is, they adopted idol worship.
✦ Some people denied the finality of Prophethood.
They began to accept Musaylimah the Liar and Aswad al-Ansi as claimants to Prophethood and became their followers.
Abu Bakr (radi Allahu anhu) fought against both these groups and put an end to them.
In fighting against them, Umar (radi Allahu anhu) was also his supporter.
✦ There was a third group as well, which differentiated between prayer and zakat.
Their stance was that after the passing of the Messenger of Allah (sallallahu alayhi wa sallam), it was not necessary to give zakat to his successor.
Regarding fighting against them, Abu Bakr and Umar (radi Allahu anhuma) had a difference of opinion, which is mentioned in the aforementioned ahadith.

(2)
In reality, these people were rebels, but at that time they were not referred to by the name of rebels, because they were included among the group of apostates.
On this basis, they too were counted among the apostates.
In the era of Ali (radi Allahu anhu), since there was no such mixture, they were declared rebels and war was waged against them.
Abu Bakr (radi Allahu anhu) made an analogy between zakat and prayer, the denial of which is, by consensus, disbelief, and Umar (radi Allahu anhu) argued from the generality of the hadith.
Abu Bakr (radi Allahu anhu) did not rely solely on analogy, but also strengthened his position with the words “the right of Islam.”
After this clarification, Umar (radi Allahu anhu) was also satisfied.

(3)
Imam Bukhari (rahimahullah) has deduced from this hadith the obligation of zakat, which is clearer than the sun.

(4)
It should be noted that there is a narration from Ibn Umar (radi Allahu anhu) that the Messenger of Allah (sallallahu alayhi wa sallam) said:
“I have been commanded to fight the people until they testify that there is no deity worthy of worship except Allah and that Muhammad (sallallahu alayhi wa sallam) is the Messenger of Allah, establish prayer, and pay zakat. When they do this, they have protected from me their wealth and lives except for the right of Islam, and their inner reckoning is with Allah.” (Sahih al-Bukhari, al-Iman, Hadith: 25)
This hadith was not present in the mind of Abu Bakr (radi Allahu anhu); if he had remembered it, he would have presented it instead of analogy, and neither was this hadith before Umar (radi Allahu anhu), otherwise, in its presence, he would not have relied on the generality of the hadith.
It is quite possible that Abdullah ibn Umar (radi Allahu anhu), from whom this decisive hadith is narrated, was not present at the time of the discussion and debate; if he had been present, he could have presented it and immediately ended this dispute.
In any case, paying zakat is obligatory, its denial is disbelief, and making an interpretation regarding its payment is a cause for war and fighting. Accordingly, Imam Bukhari (rahimahullah) has established a chapter on this hadith with the following words:
“To fight against one who, by denying the acceptance of obligations, is attributed to apostasy.” (Sahih al-Bukhari, Istitabah al-Murtaddin, Chapter: 3)