A simple model for a letter of reference to be signed by previous landlord and given to tenant who's relocating elsewhere.
To Whom it May Concern:
Please be informed that Name was a tenant of my apartment at Address in City from Start Date to End Date. During that time Name kept the apartment neat and clean, was considerate of his neighbors and paid his rent on time.
Please feel free to call me at phone number or write me at Email address if you'd like additional information regarding their desirability as a tenants in one of your properties.