To [Recipient name]
Dear [Recipient name]
This letter is to acknowledge that I, [Your name] have borrowed a sum of [Amount] from [Lender name] for a period of [Number] weeks. This money is to be repaid to the lender by [Date]. The money has been borrowed for the purpose of [Reason] by the borrower. There is no interest charged on the amount taken by the borrower after the decided time has elapsed.
If the borrower fails to repay the loan on the given date a penalty of [Decided penalty] should be carried out according to the agreement.