I am trying to find out where this quote is referenced at in books in my library. How can I do that?
For if no one can forgive sins but God alone, while the Lord remitted them and healed men [people], it is plain that He was Himself the Word of God made the Son of man, receiving from the Father the power of remission of sins; since He was man, and since He was God, in order that since as man He suffered for us, so as God he might have compassion on us, and forgive us our debts, in which we were made debtors to God our Creator.
Irenaeus, Against Heresies 5.17.3