Kesubos 19b - Receipt for partial payment

If a borrower repays part of the loan, is the lender required to write him a receipt or return the contract? The gemara says that there is a machlokes whether a lender holding on to a contract that has already been payed is a violation of maintaining in your home an "avlah". Tosafos explains that really all agree that until the borrower finished paying off the debt and even finished paying off the expenses of writing the contract, the lender has the right to hold on to the contract without even writing a receipt. The machlokes is only if after every penny of expenses has been payed, it would qualify as an avlah (see tosafos d.h. zimnin, carefully). The Maharam Shif points out from here that the lender can continue to hold on to the contract until every penny has been payed, and is not responsible to write a receipt for the partial payment that was already received. The Shach (C.M. 57:6) agrees. However, Korban Nesanel (4) argues based on a gemara in Baba Metziah 68a where there is a concern that a partially payed contract may fall in the hands of inheritors and they will not realized that it was already partially payed, and will collect the entire sum. Therefore, the korban nesanel says that the lender can only continue to hold on to the contract after receiving partial payment if he writes a receipt for the borrower for the amount that has been payed.