Bava Metzia 65 - Early Payment is Allowed

One who rents out his property may increase the rent for payment that is delayed, but one who sells something may not increase the purchase price for payment that is delayed.
For example, if one rented a house to someone and said, "If you pay me for the year in advance - 10 sela, but if you pay every month, 1 sela a month" - the rent is the true price, and the discount is given for paying early. However, if he sold a field, the money is owed right away, and paying more later is a reward for waiting for money, which is prohibited.