Muslim

Hadith Commentary:
By mentioning these chains of narration, the purpose of Imam Bukhari rahimahullah is to show that there are many differences in this hadith: some say the questioner was a man, some say it was a woman; some mention fasting for a month, some for fifteen days; some say it was a fast of vow (nadhar), and so on. For this reason, Imam Ahmad and Layth have considered it permissible to observe a fast of vow (nadhar) on behalf of the deceased, but not the fast of Ramadan (i.e., they do not consider it correct to observe the Ramadan fast on behalf of the deceased). (When this opinion is not correct, it is necessary to observe the remaining fasts on behalf of the deceased.)

I say that these differences do not bring any deficiency to the hadith as long as its narrators are trustworthy. It is possible that these were different incidents and that there were multiple questioners.
(Wahidi)

Hadith Commentary:
(1)
Imam Bukhari rahimahullah has narrated various chains of transmission for this hadith of Ibn Abbas radi Allahu anhu. In some versions, the questioner is mentioned as a man, while in other narrations, the one asking is a woman. Some mention fasting for a month, while others mention fifteen fasts; in some, there is clarification that these were fasts of a vow (nadhar). However, these differences do not affect the validity of the hadith. It is possible that these were different incidents and that there were multiple questioners. In any case, it is established that fasting can be performed on behalf of the deceased, and Hajj can also be performed on their behalf.

(2)
The scholars have reconciled these various narrations as follows: A man came to the Messenger of Allah sallallahu alayhi wa sallam, and with him was a woman. The deceased was their sister, who was referred to as "mother" (umm) figuratively, because she was older than both of them. She had fifteen fasts of vow (nadhar) and fifteen missed (qada) fasts due, making a total of one month. And Allah knows best.

Note: The aforementioned narrations are reported from Aisha and Ibn Abbas radi Allahu anhuma, whereas in the books of hadith, the legal verdict (fatwa) of both these companions is contrary to the hadith they themselves narrated. Among the Hanafis, it is a well-known principle that when a narrator’s legal verdict contradicts the narration he transmits, then according to him, that narration is considered abrogated, and thus these narrations are not acted upon. Accordingly, it is narrated from Aisha radi Allahu anha that she said: Do not fast on behalf of the deceased, rather feed (the poor) on their behalf. (Al-Sunan al-Kubra lil-Bayhaqi: 4/254) Similarly, it is narrated from Ibn Umar radi Allahu anhu that no person should fast on behalf of another. (Jami‘ al-Tirmidhi, Kitab al-Sawm, Hadith: 718)

Firstly, the hadith scholars have critiqued these reports, and secondly, the primary consideration is given to the narration they transmitted, and their legal reasoning (ijtihad) holds no weight in comparison to the narration itself. (Fath al-Bari: 4/247)

1:
This hadith is evidence that if a person dies and there is a fast due upon him, then his guardian should fast on his behalf. This is the statement of the hadith scholars (muhaddithin), and this is the preferred (rajih) opinion.

(1) It is understood from this that fulfilling the rights of Allah holds a status more important and higher than fulfilling the rights of the servants, even though obtaining forgiveness for the rights of the servants is difficult.

(2) If Hajj was obligatory (whether by Shari'ah or by vow) upon the deceased and he was unable to perform it during his lifetime, then Hajj should be performed on his behalf from his wealth. Similarly, expiation (kaffarah), zakat, and debts should also be paid, even if the entire wealth of the deceased is consumed. The one-third (thulth) restriction will not be considered because their status is not merely that of a bequest (wasiyyah).

(3) From this narration, an argument has been made for the permissibility of analogy (qiyas), but in reality, the Prophet (sallallahu alayhi wa sallam) had no need for analogy. Revelation was ongoing, and analogy is only applied in matters for which there is no explicit text. The statement of the Prophet (sallallahu alayhi wa sallam) itself is a text (nas). Analogy can only be done by a follower (ummah member) who does not have a clear text (explicit statement of Allah and His Messenger).

(4) A person may make a vow (nadhar) to perform Hajj even if he has not performed the obligatory Hajj. Then, when he performs Hajj, his obligatory Hajj will be fulfilled, and afterwards he will perform the Hajj of his vow. This is the opinion of the majority. There is another opinion contrary to this, that his first Hajj will be counted as the vowed Hajj and the second as the obligatory one, and there is also an opinion that his Hajj will suffice for both, but this opinion does not seem correct.

(5) This hadith is evidence for the majority of the scholars that if a person deliberately abandons prayer, then making up (qada) for it is obligatory upon him, because this is a debt owed to Allah.

(6) A scholar and mufti should adopt such a manner of explaining an issue that the questioner fully understands it, and no kind of thirst (lack of clarity) remains, and he becomes completely satisfied.