What is the way to secure the future after retirement without resorting to prohibited types of insurance?

If the inquirer desires a means free from doubt, they should resort to traditional methods based on economy and investment, such as economizing on spending and directing the remaining money towards investment in a permissible field to generate lawful profit. If they are unable to invest themselves, there is sufficient provision for them in contracts of Mudarabah (profit-sharing) and legitimate companies. Among the possible means is to search for a fund based on cooperative Takaful (Islamic insurance); if one is found to be compliant with Sharia regulations, it is permissible to subscribe to it.