Here’s another template you can use to write a letter denying a salary increase.
I received your salary raise request and would like to frankly discuss it with you. You definitely perform excellently sometimes. However, I need to see your consistency in your work before I consider giving you a raise.
Know that I’m not reprimanding you. Overall, the company and I are pleased with your overall performance. But to move on to the next stage of your employment here, we’d like to see that you’re consistent in exerting great effort for the company.
You are welcome come by if you need to discuss this further.