Apart from voluntary actions, is it permissible to donate the reward of farḍ & wājib acts?
There is no doubt in the permissibility of īṣāl e-thawāb (donating reward) for optional deeds. Whether farḍ & wājib acts are permissible to donate? The scholars have differed in their opinions. However, many have opined towards its permissibility. This is because when doing īṣāl e-thawāb (donating reward), the recipient only receives reward, they are not absolved from that certain act.
ʿAllāmah Ibn Nujaym writes, “The fuqahā (jurists) addressing the ruling of īṣāl e-thawāb (donating reward) unconditionally, proves that there is no difference between donating the reward of a farḍ or wājib action and donating the reward of an optional deed. Thus, if after performing a farḍ ṣalāh, it’s reward is donated then it is correct. However, the recipient will not be absolved from that ṣalāh.”
(Adapted from Ṣadaqa-e-Jāriyah wa Īṣāl e-Thawāb ke Faḍāil wa Aḥkām by Muftī Muhammad Riḍwan.
Published by Kutub Khāna Idāra Gufrān, Rawalpindi.)