Plato, Meno 79d

εἰ γὰρ καὶ μέμνησαι, ὅτʼ ἐγώ σοι ἄρτι ἀπεκρινάμην περὶ τοῦ σχήματος, ἀπεβάλλομέν που τὴν τοιαύτην ἀπόκρισιν τὴν διὰ τῶν ἔτι ζητουμένων καὶ μήπω ὡμολογημένων ἐπιχειροῦσαν ἀποκρίνεσθαι. καὶ ὀρθῶς γε ἀπεβάλλομεν, ὦ Σώκρατες. μὴ τοίνυν, ὦ ἄριστε, μηδὲ σὺ ἔτι ζητουμένης ἀρετῆς ὅλης ὅτι ἐστὶν οἴου διὰ τῶν ταύτης μορίων ἀποκρινόμενος δηλώσειν αὐτὴν ὁτῳοῦν, ἢ ἄλλο ὁτιοῦν τούτῳ τῷ αὐτῷ

And I daresay you remember, when I answered you a while ago about figure, how we rejected the sort of answer that attempts to proceed in terms which are still under inquiry and has not yet been admitted. Yes, and we were right in rejecting it, Socrates. Well then, my good sir, you must not in your turn suppose that while the nature of virtue as a whole is still under inquiry you will explain it to anyone by replying in terms of its parts, or by any other statement