Where did Aquinas say that the "greatest penalty of sin is the loss of the sense of sin"? Can someone point to me where St. Thomas Aquinas said that the, "greatest penalty of sin is the loss of the sense of sin"?

I heard this from Catholic Answers Live last week.
The Summa Theologiae and in the third book of the Summa "Contra Gentiles"

CAtholic answers (I did not hear the program) may have been paraphrasing the concept of Aquinas's view of original justice and the effect it has on our inability to recognize sin.