Mass. Gen. Laws ch. 140, § 90C

Upon payment of any money by the borrower, the lender shall at the request of the borrower give him a receipt stating the date of payment, the amount paid, the amount applicable to interest on the loan and the amount applicable to the principal. Such receipt shall be signed by the lender or his duly authorized representative. If a lender refuses, on written demand sent by registered mail, to give such receipt, he shall forfeit all interest on the principal sum.