I was hired but became disabled, so outsourced the job but paid cash. Now SSA asks for explanation, it was 5 years ago. What to do? Affadavit?

Was hired as an on-call administrator. Was not able to do the job, so hired an assistant and administrator to do the job for me. The job just needed my certification. However, just filed for disability, and since the checks came to me, it came up as extra monies on my taxes. Due to the situation, the job was oursourced informally and I paid the money cash. Taxes were paid and all monies were paid to these people. However, I no longer have records. To explain the only thing I can think of is an affadavit. But how to explain effectively?