On the ruling regarding revoking an endowment.

The Shaykh : We will mention something regarding the endowment. First: Is the endowment a binding contract? In other words, if a person endows something, does it become an endowment immediately and become binding such that he cannot retract it? The answer is: Yes. If you say, "This is an endowment," it becomes binding immediately, and you cannot retract it. This is because the endowment is like freeing a slave. Just as a person cannot retract the freeing of his slave once he has freed him, so too, if he endows his property, he cannot retract it.