The quote you want is in the second book, "The Sieve and the Sand", when Montag visits Faber at his home and asks him to help him understand what he reads. Beatty has confused him by telling him that books will create chaos in the society, and Montag wants to know more.
My edition of the book has the quote on page 82 at the very top of the page. It is the first line. Your edition of the book may have it on another page but it should be close. The paragraph starts with
"It's been a long time, I'm not a religious man." (pg 81)
Faber thinks of himself as a coward because he did nothing and said nothing when he saw the way things were going. He says,
"Mr. Montag, you are looking at a coward. I saw the way things were going, a long time back I said nothing. I'm one of the innocents who could have spoken up and out when no one would listen to the 'guilty, but I did not speak and thus became guilty myself." (pg 82)