You are correct that you are not required to issue a 1098 form to the borrower if you are not in business of lending. Write a private letter listing amount of interest that the borrower paid you on the loan for 2014.  As to the social security number - yes, you should include the SSN number on the letter. In fact, the borrower should have had your SSN number so that he could property report the interest that he paid on a seller financed loan.