This is to acknowledge your letter of [date] You are definitely to be commended for your progress during the past two months.
I do believe, however, that your recent request for a raise is premature. I would suggest that it would be more appropriate to discuss a salary increase after you have worked here for six months. If you continue on the same path, I am certain that your timely request will be given careful consideration.
You are doing a fine job, keep up the good work!