[Ruling on One Who Swore to Make His Wealth a Waqf]

Answer—and Allah is the One who grants success: The scholars of the madhhab have said: If all that issues from the wāqif is the bare wording of “waqf,” and it is not known that he intended qurbah, then his waqf is not valid.
This can be supported by saying: The default is that wealth remains the property of its owner, and it does not leave his ownership except by a [sound] indication. In the Law, the indication that removes property from ownership by way of waqf is that, together with the wording, it be seeking the Face of Allah and the Hereafter—as occurred in the waqf of the Commander of the Faithful—or that there be wording to that effect, as in: “As for Khālid, he has held his armor and horses in the path of Allah,” or [designations] for the Muslims, or for kin, or for parents, as appears in other narrations.

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