Is it permissible for the endower to change an endowment he made for his daughters by adding himself, his wife, and his descendants, especially since he oversees his endowment and the change is for the sake of benefit?

The majority of jurists believe that the waqf (endowment) is a binding contract as soon as its conditions are met. The endowed property thereby exits the ownership of the endower, and their right to dispose of it through sale, gift, or inheritance is relinquished, as stated in the Prophet’s (peace be upon him) hadith to Umar ibn al-Khattab (may Allah be pleased with him): "Donate its essence, and it is not to be sold, gifted, or inherited."

According to Abu Hanifa, the waqf is permissible but not binding, and the endower may revoke it. However, the fatwa (legal ruling) within the Hanafi school has settled on the view of Abu Yusuf and Muhammad, which holds it to be binding.

The binding nature of the waqf necessitates that its purpose or beneficiaries cannot be changed. It is not permissible for the endower to stipulate for themselves the right to change the beneficiaries after establishing the waqf, because this condition contradicts the very essence of the waqf. Accordingly, the addition made by the questioner to the waqf, including themselves, their spouse, and their offspring, is not valid.