Is it permissible to donate the pension of a deceased father, which a mentally and physically disabled sister receives, to another sister who is experiencing financial hardship, given that the disabled sister is not in need of this pension?

If the pension is a gift from the state or the employer, then it is a right for those designated by the granting entity. If it is specifically allocated for the disabled daughter, then it is not permissible to donate any part of it to others. However, if it was deducted from the father's salary during his lifetime, then it is part of the inheritance and is to be divided among the heirs according to their prescribed share in Islamic law. It is not permissible for anyone to donate any part of the disabled sister's share from it.