First Paragraph - Personal Reference
I have known John Smith in a personal capacity for over ___ years and have found him to be honest, reliable, conscientious and courteous. I am confident that he will prove to be an asset to your company.
Alternative First Sample Paragraph - Business Reference
I have known John Smith in a professional capacity for over ___ years and would confirm that he currently holds the position of _______ in Zzedro Inc.
Second Paragraph: I would confirm that the his/her performance and attitude has been satisfactory / good / excellent during his employment.
Closing Sample Paragraphs
I trust that the information provided will be of help and assistance.