Is money earned from a private business, which its owner sometimes managed during official working hours without affecting his performance, considered permissible, or is it rightfully the company's? And is it permissible to donate this money with the intention of dedicating its reward to the company if it is rightfully theirs, or with the intention of acceptance from Allah if it is rightfully his?

Whoever works for an entity or a company is not allowed to work for himself during official working hours except with the permission of his employer. If he works without permission and harms his employer, he must pay the value of the damage incurred, or pay what he earned as wages from the other work. It is not permissible to give as charity what must be paid to the employer, because the rightful owner is present and his right can be restored to him.