What arguments do the Church Fathers make for nocturnal emissions not being a sin? I've run across claims (although I'm having trouble digging them up again; I might be thinking of the implications in this reddit thread) that Augustine and Cassian were almost the only early Christian writers (before the medieval period, anyway) to deal with the problem of nocturnal emissions, and that both defended the phenomenon as being basically not sinful. Unfortunately, I can't seem to find their exact writings; translations usually seem to leave out Book VI (fornication/impurity/lust) of Cassian's Institutes (and for  that matter, his Conference 22 about Nocturnal Illusions), and shuffling through Augustine's writings on the general topic doesn't seem to turn up anything obvious. Perhaps I'm just looking for the wrong terms or at the wrong writings?

In particular, I'd like to analyze the reasons they gave for considering wet dreams to be non-sinful; did they focus solely on the involuntary aspect, or were there other considerations? Later it seems there was an occasional mention of nocturnal emissions without corresponding lustful dreams (and how this marked spiritual progress); how early was this distinction made?
Augustine addresses this question in his commentary On the Literal Meaning of Genesis: Book XII, section 31 (or 15 depending on your version).  He ascribes the lack of sin to the involuntariness.  He notes that well-disposed, chaste souls have some merits which "shine out even in dreams," although even chaste people may have nocturnal emissions.

John Cassian takes this up in Conference 22 of his Conferences, but it is hard to find a version that does not omit that conference.