Now passive scandal is not always a mortal sin, but is sometimes venial, as stated above (A. 4). Therefore passive scandal may be found in perfect men.
 Thomas Aquinas, Summa Theologica (1274). copy citation

add
Author Thomas Aquinas
Source Summa Theologica
Topic sin state
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/18755/pg18755-images.html

Context

“2:18: "We would have come to you, I Paul indeed, once and again; but Satan hath hindered us." Therefore even perfect men can suffer scandal.
Obj. 3: Further, even perfect men are liable to venial sins, according to 1 John 1:8: "If we say that we have no sin, we deceive ourselves." Now passive scandal is not always a mortal sin, but is sometimes venial, as stated above (A. 4). Therefore passive scandal may be found in perfect men. On the contrary, Jerome, in commenting on Matt. 18:6, "He that shall scandalize one of these little ones," says: "Observe that it is the little one that is scandalized, for the elders do not take scandal."
source