Mass. Gen. Laws ch. 236, § 35: Redemption of mortgage paid by creditor or purchaser

Section 35. If the creditor or, in case of a sale, the purchaser pays the debt due on a mortgage to which the land levied on is subject, the judgment debtor may redeem the mortgage from the creditor or purchaser at the time when, and upon the terms upon which, he might have redeemed it from the mortgagee if no execution had been levied. If the debtor does not so redeem the mortgage, the creditor or purchaser shall hold the land as an assignee of the mortgage and free from any right of redemption, notwithstanding the debtor has redeemed or offered to redeem the right taken on the execution. If the debtor does not within one year after the levy redeem the right taken on the execution, the creditor or purchaser shall hold the land against the debtor, notwithstanding the debtor has redeemed or offered to redeem the mortgage.