Is the piece of agricultural land that the mother bought with money she took from the father without his knowledge considered permissible (halal) or forbidden (haram), knowing that the father is financially capable and they live in a dilapidated house on the verge of collapse?

A home is essential for human life. When a father provides housing for his wife and children that he himself inhabits, then there is no further religious obligation upon him, unless he wishes to expand their living space and is capable of doing so. This is commendable, based on the Prophet's (PBUH) saying: "Among the happiness of a person are: a righteous neighbor, a comfortable mount, and a spacious dwelling." Owning a home is not a necessity as long as housing is available through rent, gift, or loan.

If the husband is fulfilling his obligatory financial support, then it is not permissible for his wife to take money from him without his willing consent, based on the Almighty's saying: {unless it be trade by mutual consent between you} and the Prophet's (PBUH) saying: "The property of a person is not lawful [for another] except with his willing consent."

Therefore, any money collected by the mother from the father to buy land is not permissible except with his knowledge, because it is not permissible to take without his knowledge, unless it is for basic necessities that fall short. The father must be informed, and the land must be registered in his name. If it is in the name of the mother or one of the children, this must be changed. If the father has passed away, the land becomes an inheritance to be divided according to the rules of inheritance, unless the heirs agree on something specific.