Dear Pradanya,
Are you looking forward to issue him an experience certificate and relieving letter ? How are you planning to issue this termination letter to him ? Even if your employee is terminated, please don't issue any reliving document sharing the termination of services.
Let the discontinuity of the services, remain an internal process. Issue a normal relieving letter with his employment details.
If you avoid mentioning any details about the termination, you help him build a career beyond your firm.
No matter whatever, the reason for termination is, a misfit somewhere is an hi-performer somewhere else. Performance of an employee is often a result of the environmental support he receives. Hence, putting non-performance as a reason for termination in the letter, might back fire on you as an employer.
Please keep this in mind, while processing the document. Wish you all the best !