Sifrei Devarim
It is not written "Mine is revenge and I shall pay," but "Mine is revenge and payment." I pay for their deeds and for the deeds of their fathers before Me, as it is written (Isaiah 65:6-7) "I will repay into their bosom, your sins and the sins of your fathers together … and I will mete out (payment for) their deeds first into their bosom."