Full Idea
Carneades used to say that not even Apollo could tell any future events except those whose causes were so held together that they must necessarily happen.
Gist of Idea
Even Apollo can only foretell the future when it is naturally necessary
Source
report of Carneades (fragments/reports [c.174 BCE]) by M. Tullius Cicero - On Fate ('De fato') 14.32
Book Reference
Cicero: 'On Fate, Stoic Paradoxes, Oratory', ed/tr. Rackham,H. [Harvard Loeb 1942], p.229
A Reaction
Carneades is opposing the usual belief in divination, where even priests can foretell contingent future events to some extent. Careneades, of course, was defending free will.