Is money acquired from selling goods to a manager at a price higher than their original cost without his knowledge, or from receiving a percentage from the source, considered unlawful money, knowing that this is not part of the job's duties?

If your role in the company is not to purchase and select goods, then there is no harm in you buying and selling them to your company, or acting as a middleman between the seller and the company. However, you must inform the manager that you are financially benefiting from this process, because an agent or broker should not deceive the one for whom he works by making him believe he is donating when he is not. It is not necessary to inform him of the amount of profit; it is sufficient for him to know that you are benefiting from a commission or selling goods to the company.