Is it permissible for one to contribute to an endowment (waqf) with the intention of earning reward for those who have non-financial rights over him on the Day of Judgment, and is it permissible to include oneself in the intention by saying: "This endowment is for me and for those who have rights over me," and is it valid for the reward of the endowment to return to me alone after their rights have been fulfilled?

We have previously explained that being absolved of people's intangible rights is achieved by seeking their forgiveness if possible without causing harm. Otherwise, sincere repentance, praying for them, seeking forgiveness for them, and speaking well of them suffice. It is not necessary to donate the reward of an endowment to them, though there is no harm if you do so. Similarly, there is no harm in sharing the reward with them. Your absolution from people's intangible rights is not originally related to an endowment. If you intend for the reward of the endowment to be for you alone, after their rights have been fulfilled, there appears to be no impediment.