Question: And does this woman have the right to dedicate some of her wealth as a waqf for a mosque or some public benefit, placing the authority over that under her husband and in his hand? And does her cousin [the son of her paternal aunt] have the right to object to her?
Answer: If the woman is in good health and well-being, then she has the right to do with her wealth whatever she wishes, whether waqf, vow, sale, or transfer of ownership. Whatever she does of that or of other forms of disposal is valid, and no one has the right to object to her – neither the husband nor anyone else.
As for if she does that while in her death-illness, then her disposal is valid only in one-third of her wealth, and not in more than that, except with the permission of her heirs.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2