[Ruling on Whether Charity Reaches the Deceased]

Answer—and Allah is the One who grants success: It will reach the deceased, and its reward will benefit him. The evidence for this is:
1. It is related that the Prophet (May Allah bless him and his family and grant them peace) heard a man pronouncing the talbiyah on behalf of Shubruma. He (May Allah bless him and his family and grant them peace) said to him, “Who is Shubruma?” The man replied, “A brother of mine.” The Prophet (May Allah bless him and his family and grant them peace) said, “Perform ḥajj for yourself, then perform ḥajj on behalf of Shubruma,” or as he said.
2. It has come in the reports that the Prophet (May Allah bless him and his family and grant them peace) offered a sacrifice on behalf of his community.
3. In the Ṣaḥīfah of ʿAlī b. Mūsā al-Riḍā—on the authority of the Prophet (May Allah bless him and his family and grant them peace)—it is mentioned that whoever passes by cemeteries and recites Sūrat al-Ikhlāṣ eleven times, then gifts its reward to the inhabitants of the cemetery … and so on.
4. Al-Bukhārī and Muslim relate that a man said to the Prophet (May Allah bless him and his family and grant them peace), “My sister vowed to perform ḥajj, and she has died.” He said to him, “If she had a debt, would you pay it off for her?” He replied, “Yes.” He said, “Then pay Allah’s right—He has more right to be paid.” (As cited in al-Iʿtiṣām.)
All of this indicates that the reward of charity reaches the deceased in absolute terms—whether from a child or from someone else.
Yes, what we have mentioned specifies the generality of His saying, Exalted is He: “And that there is not for man except that [good] for which he strives.” [al-Najm:39]
If it is said: It is related from the Prophet (May Allah bless him and his family and grant them peace), “When the son of Ādam dies, his deeds are cut off except from three: a righteous child …,” etc.
We say: There is no contradiction between what we have stated and this ḥadīth. What we have cited does not pertain to the deceased’s own actions; rather, it pertains to the actions of others whose reward and benefit reach him by way of connection and charity—not by way of his own deeds, for those have indeed ceased.
Likewise, there is no contradiction between the verse and what we are discussing here, for the meaning in our case is that what reaches the deceased does so not by entitlement through his striving, but by way of connection, charity, and gracious bestowal—not by means of his own striving. Reflect upon this.
There is also the ḥadīth narrated from Ibn ʿAbbās: a man came to the Messenger of Allah (May Allah bless him and his family and grant them peace) and said, “O Messenger of Allah, my sister vowed to perform ḥajj, and she has died.” He said, “If she had a debt, would you pay it off for her?” He replied, “Yes.” He said, “Then pay Allah’s right—He has more right to be paid.” This supports what we have mentioned. And Allah knows best.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1