Simply replace the unfilled areas such as "__" and "_[date]_" with your information.
I would like to let you know that I have decided to sell my _[Business/Property/Practice]_. After having my _[Business/Property/Practice]_ for _[#]_ years, i have developed solid and productive relationships with both clients and partners. After much thought, I've realized that the timing is right for me to move on.
I would like to introduce you to _[name]_, who will be taking over my position effective _[date]_. Rest assured _[he/she]_ is a very competent _[businessman/woman/etc.]_ with _[#]_ of years experience behind _[him/her]_. It is important to me to find a perfect fit for my clients and I feel confident that _[name]_ will be very knowledgeable and a pleasure to work with.
I thank you for your business support over the years. It was my pleasure to have been of service to you and I wish you continued success in the years to come.