Is it permissible for an employee to take a bonus that his employer promised him without the employer's knowledge, and what is the legal ruling on that?

It is permissible to take the agreed-upon reward without the knowledge of the owner of the money if the employer had promised it for extra work beyond the job, and then procrastinated. This is considered obtaining one's right by force. However, if the work was part of the job or volunteered, and a reward was promised and then rescinded, it is not permissible to take from his money, because a mere promise of a gift does not transfer ownership Islamically.