Terminating an employee in case of working for a competitor without permission

An employee was found to be working on his weekly day off for a competitor.

I (the employer) cannot prove that the employee received any monetary consideration for his work but the fact that he offered his services to a competitor itself is deeply disturbing to the environment of trust and integrity in the company.

Needless to say, this employee cannot be trusted in the future. The incident in question was witnessed by someone who knows me personally and the said person called me from the site and reported it to me.

It is possible that the employee has been doing this regularly over time but happened to get noticed this time. Can this employee be terminated under Article 120 of the UAE Labour Law?

If not, what remedies are available to the employer?