Is a gift of land valid if a grandmother gifted it to her son without the knowledge of her other children, and do they have the right to object to this gift after the grandmother's death?

If a mother singles out one son for a gift, excluding her other children, this is forbidden unless there is a legitimate Sharia-compliant reason. The evidence for this is the Prophet's (peace be upon him) statement: "Indeed, I do not bear witness to injustice." Therefore, the mother was obligated to return the gift, or to give an equal gift to her other children. However, now that she has passed away, if the son did not take possession of the gift before the mother's death, then the gift becomes void and reverts to an inheritance to be divided among the heirs. But if the son took possession of the gift during her lifetime and disposed of it, then the gift remains valid upon her death, despite the injustice it contained. The land then belongs to the one to whom it was gifted if the gift was valid and executed; otherwise, it belongs to all heirs. It is advisable to refer to the Sharia courts in case of a dispute.