Is it permissible to invest money left in trust (amanah) in trade, while preserving it and returning it upon demand, and bearing any loss?

Allah Almighty and His Messenger, peace and blessings be upon him, commanded that trusts be returned to their rightful owners. Therefore, you must return the money to its owner by searching for him and attempting to contact him. If you despair of reaching him, keep his money until he requests it, or donate it on his behalf after exerting the utmost effort to find him. If its owner comes later, inform him of what you did; he may then approve the charity, and its reward will be his, or he may reclaim his money, and the reward for the charity will be yours.