Is pension money (retirement) forbidden or permissible, and is one sinful for consuming from it if it is forbidden?

If the father participated in a commercial insurance system or savings funds based on a commercial system, then he is only entitled to what he contributed. Anything in excess of that is unlawful wealth that must be disposed of by spending it on the welfare of Muslims or on the poor and needy. It is not permissible for the recipient to benefit from it unless they are poor. However, if the participation was in a cooperative Takaful insurance system, or if the employer, whether governmental or non-governmental, provides a gift to employees, then there is no harm in benefiting from it. If you are poor and have no source of income other than your father's pension, then there is no harm for you in benefiting from the excess amount over the installment, to the extent of your needs.