Good question. The voice and e mails are evidence of the $13,500 loan that you made your friend by way of an admission from him. I would e mail him a confirming note about the loan to be on the safe side and send him a promissory regarding the $13,500 loan for him to date, sign and return.You can get these forms on line. Make sure you state the amount of the loan, due date and interest rate. Also distinguish if monthly payments are to be made or not.