[Ruling on transferring a waqf by selling the “hand” (possession right) over it]

Answer—and Allah is the One who grants success: If the first man has expenses and losses for which the price is intended as compensation, then the sale is valid; otherwise it is not permissible, and the price is unlawful—because the sale is conducted by one who is merely a participant/possessor, not an owner, and he takes the price without a countervalue. Allah Most High says: “Do not consume one another’s wealth unjustly.” [An-Nisāʾ:29].
Thus have the jurists of the school said regarding transferring testamentary trusts from one hand to another, as in the marginalia on Sharḥ al-Azhar.
That said, it may be said: There is no impediment to this.
And one may answer the proof they cited by saying: The seller has sold usufructs he is entitled to in the waqf, which are his property; accordingly, receiving the price is in exchange for those usufructs, and selling usufructs is permissible—as evidenced by lease (ijārah), which is the sale of usufruct.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2