You do not have to give the buyer a Form 1098 because you are not in the business of making mortgage loans. Tell him to tell his tax preparer to look at the IRS instructions for Form 1098 and Schedule A. However, you do have to give him your SSN. He has to put your name, address, and SSN on Schedule A of his tax return in order to claim a deduction for the interest that he pays to you. He also has to give you his SSN, and you have to put his name, address, and SSN on Schedule B of your tax return when you report the interest income.
