Corrupte apud Florezium, Augustine,
"Mentitur qui te totam legisse factetur"
My (literal) translation:
[Concerning Augustine] He is a liar who confesses to have read the whole [of his works].
See the full paragraph below. Normally the quote is cited to mean that there are too many works of St. Augustine for anyone to claim to be an expert. Joseph Kelly comments, however, "The famous remark of the Spanish scholar Isidore of Seville (c. 560-636), that anyone who claimed to have read all the works of Augustine was a liar, was referring not to the number of the saint's works but to their accessibility in the early middle ages." Apparently there were few libraries that had a complete collection of St. Augustine's works. Still the saying resonates with the difficultly of fully absorbing all of St. Augustine's thought.
 Full paragraph of PL 83.1109
Pro alumna alii ultique.
IV. Entit ; al., eninet.
V. Corrupte apud Florezium, Augustine,
Mentitur qui te totam legisse factetur.
Pro an quis alii ant quis. De re ipsa vide Etymo.og.
lib. vi, cap. 7, n. 3, versu 4, alii, quae loquur. Pro
ipse , alii ipsi, quod metro non congruit. Pro prudent-,
metrum desiderari ; sed videntur potius esse tres
hexametri sine ullo pentametro. De tertio versu dietum
in Isidorianis, loc. cit.
Joseph F. Kelly, "Late Carolingian Era" in Augustine through the ages: an encyclopedia Ed. Allan Fitzgerald, John C. Cavadini. (Grand Rapids: Eerdmans, 1999) p. 127.