both obligations laid down by the Law and those incurred through a vow.
They also adduce the report of Ibn ʿAbbas recorded by al-Bukhari (1953) and Muslim (1148): “A man came to the Prophet ﷺ and said, ‘Messenger of Allah, my mother died owing a month of fasting; shall I fast on her behalf?’ He replied, ‘Yes. A debt owed to Allah is worthier of being settled.’
Those who differentiate maintain that both the present hadith and the hadith of Ibn ʿAbbas relate only to vows. Ibn al-Qayyim upheld this view, saying, “No one may fast on behalf of another”—meaning the obligatory fast—“whereas a vowed fast may be observed for him.” In this way he reconciled the various narrations. Ibn al-Qayyim added that a vow is not an obligation originally imposed by the Law; rather, the person obliges himself to it, so it becomes akin to a debt he has incurred.
The rationale behind the distinction is that a vow is a voluntary commitment placed by the responsible person upon his own liability; the Law did not bind him to it from the outset. Its ruling is therefore lighter than that of an injunction directly legislated by the Law—which obliges a person whether he wills or not—while the liability can encompass both what one is able and unable to do. The inherent duties of the Law, by contrast, correspond to a person’s capacity.
The stronger opinion is that the hadith is general, embracing both categories: obligations established by the Law itself and those arising from a vow.
Any reports or traditions that appear to conflict with this hadith are not weighty enough to counter it.
Moreover, numerous authentic texts of the Sunnah support its purport. The Khathʿamite woman said to the Prophet ﷺ, “Shall I perform the pilgrimage on behalf of my father?” He answered, “Yes.” [Al-Bukhari 1417; Muslim 2375]. Likewise, the Juhayni woman said, “My mother vowed to perform the pilgrimage but died before doing so. May I perform it for her?” He replied, “Yes, perform it for her. Fulfil Allah’s dues, for Allah is most worthy of being repaid.” [Al-Bukhari 6771; Muslim 1939]. Saʿd ibn ʿUbada also issued a verdict that charity should be given on behalf of his mother when she died without giving the charity she had intended. All of these reports are found in the two Ṣaḥīḥ collections.