What is the Sharia ruling on the action of a mother who wrote to her son a portion of the house that his father had written to her before his death, and refused to give her daughter anything from it except after her death, justifying this by saying that her son is the one who spends on her?

It is not permissible for parents to prefer one child over another in giving gifts; rather, they must be just between them, male and female, based on the saying of the Prophet, peace and blessings be upon him: "Be mindful of Allah and be just among your children," and "Be equitable among your children in giving gifts. If I were to prefer anyone, I would prefer women." An exception to this is if there are special circumstances that necessitate helping one of the children, such as if they are providing for the family. The father's will bequeathing the house to his wife is not valid because she is an heir, unless the other heirs agree, based on the saying of the Prophet, peace and blessings be upon him: "There is no bequest for an heir." However, if the writing was an immediate gift that was taken possession of, and the father was competent to dispose of it, then it is considered a valid gift.