What is the ruling of Islamic law on investing money donated to the Mujahideen, with the aim of developing it to become a continuous resource for them, provided that all profits and the principal are transferred to them upon completion?

The agent must adhere to the limits of the agency and not act except as authorized by the principal, either explicitly or implicitly through custom. If the donating entity or donor does not authorize the investment of funds, the agent is not permitted to do so. If the agent does invest the funds, they are liable for any damage or loss incurred. If the agent believes that investment is in the interest of the beneficiaries, they must seek permission from the donor or beneficiary before proceeding.