The Ruling on Performing Hajj as a Supererogatory Act on Behalf of a Capable Man

Answer—and Allah grants success: That is valid and permissible, because Hajj and ʿUmrah are among the acts of worship in which deputization is valid. In a voluntary act, the stringent conditions of the obligatory Hajj—such as despairing of being able to perform it oneself—are not required. Allah Most High obligated the capable person to perform Hajj himself in His saying: “And [due] to Allah from the people is a pilgrimage to the House—for whoever is able to find thereto a way.” [Āl ʿImrān:97]. Therefore, deputization is not valid nor sufficient in the obligation except upon lack of capacity and despair of attaining it.
This rationale does not exist in supererogatory acts; thus the one on whose behalf it is done is not obliged to perform it himself.
Moreover, the norm in the Sharīʿah is lenience in supererogatory acts in ways not allowed in obligations—such as performing nāfilah while mounted wherever it faces, performing nāfilah seated, and the nāfilah of charity, which is valid beyond the eight zakāh categories and even for a non-belligerent disbeliever.
Further, what appears to me is that a Muslim may donate the reward of any supererogatory act—prayer, fasting, charity, Hajj, ʿUmrah, remembrance, Qurʾān recitation, teaching knowledge, guiding the lost, fulfilling a believer’s need, and other forms of righteousness—to whomever he wishes among the believers: a parent, child, brother, relative, or distant person, or to the souls of the Prophet (May Allah bless him and his family and grant them peace) and his family (peace be upon them). He does so by intending—before commencing the act—that he donates its reward to so-and-so as an act of dutifulness and charity. It suffices to intend: “These two rakʿahs are on behalf of so-and-so.”
This may be indicated by what has come in the Qurʾān and Sunnah encouraging seeking forgiveness for believing men and women. Allah Most High related of the angels: “Those [angels] who carry the Throne and those around it exalt [Allah] with praise of their Lord and believe in Him and ask forgiveness for those who have believed, [saying], ‘Our Lord, You have encompassed all things in mercy and knowledge, so forgive those who have repented and followed Your way and protect them from the punishment of Hellfire. Our Lord, and admit them to gardens of perpetual residence which You have promised them, and [admit] whoever was righteous among their fathers, their spouses, and their offspring. Indeed, it is You who are the Exalted in Might, the Wise. And protect them from the evil [consequences of their deeds]. And he whom You protect from evil that Day—You will have given him mercy. And that is the great attainment.’” [Ghāfir: 7–9]
This indicates that a believer benefits from the supplication of others—his sins are expiated and he attains good deeds thereby. Righteous works such as prayer and others fall under the category of supplication in meaning—or are even more emphatic. One who, for example, prays two rakʿahs on behalf of so-and-so is, in effect, beseeching Allah and seeking from Him to increase so-and-so’s good deeds, expiate his sins, and raise his ranks.
There is no difference between supplication and seeking forgiveness, on the one hand, and performing prayer and other acts, on the other—except that the former is a verbal expression while the latter is a practical expression. Both share the essence of seeking nearness to Allah and pleading with Him to forgive so-and-so and increase his good deeds.
This is clarified by the fact that Allah Most High has called worship “supplication” in many verses, such as His saying: “So do not invoke with Allah anyone.” [al-Jinn:18]. And His saying: “Call upon Me; I will respond to you. Indeed, those who disdain My worship will enter Hell [rendered] contemptible.” [Ghāfir:60]
Yes—whatever a believer donates of his acts of worship to the soul of his believing brother, nothing is diminished from his reward—by the proof of what has come regarding one who performs Hajj on behalf of another: that three Hajj are written—one for the pilgrim, one for the deceased, and one for the executor. Indeed, it appears that he is written the reward of dutifulness and kinship, and “a good deed is [rewarded] tenfold,” so that, instead of a single Hajj, ten Hajj are written—this, if accepted—and Allah Most High multiplies beyond that for whom He wills.
This applies when the act is performed as an act of dutifulness, kinship, and charity. As for Hajj performed for a fee, only one Hajj is recorded for him, as in the report—because he did not do it as charity, but for remuneration; he took his wage in the world, and Allah Most High writes for him one Hajj out of bounty and mercy.
As for bodily obligations, their scope is narrower: none may perform a bodily obligation, such as the prayer, on behalf of another—except for Hajj, in which deputization has been authentically permitted in the reports from the Prophet (May Allah bless him and his family and grant them peace).
The scholars have differed regarding fasting: some permitted deputization, others did not.
As for obligations involving wealth and transactions, deputization therein is valid. The scholars said: whatever a legally responsible person is permitted to do himself, he is permitted to appoint an agent to do it for him. Some exceptions to this principle have been mentioned—such as reviving dead land, hunting, and the like—but what appears preferable to me is that agency in this is permissible, by the proof of what is narrated: that some of the Companions shared among themselves what would accrue to them of spoils on the Day of Badr.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1