Plato Apology 20

[20] For each of these men, gentlemen, is able to go into any one of the cities and persuade the young men, who can associate for nothing with whomsoever they wish among their own fellow citizens, 20a to give up the association with those men and to associate with them and pay them money and be grateful besides.
  And there is also another wise man here, a Parian, who I learned was in town; for I happened to meet a man who has spent more on sophists than all the rest, Callias, the son of Hipponicus; so I asked him—for he has two sons— Callias, said I, if your two sons had happened to be two colts or two calves, we should be able to get and hire for them an overseer who would make them 20b excellent in the kind of excellence proper to them; and he would be a horse-trainer or a husbandman; but now, since they are two human beings, whom have you in mind to get as overseer? Who has knowledge of that kind of excellence, that of a man and a citizen? For I think you have looked into the matter, because you have the sons. Is there anyone, said I, or not? Certainly, said he. Who, said I, and where from, and what is his price for his teaching? Evenus, he said, Socrates, from Paros , five minae. And I called Evenus blessed, 20c if he really had this art and taught so reasonably. I myself should be vain and put on airs, if I understood these things; but I do not understand them, men of Athens .
  Now perhaps someone might rejoin: But, Socrates, what is the trouble about you? Whence have these prejudices against you arisen? For certainly this great report and talk has not arisen while you were doing nothing more out of the way than the rest, unless you were doing something other than most people; so tell us 20d what it is, that we may not act unadvisedly in your case. The man who says this seems to me to be right, and I will try to show you what it is that has brought about my reputation and aroused the prejudice against me. So listen. And perhaps I shall seem to some of you to be joking; be assured, however, I shall speak perfect truth to you.
  The fact is, men of Athens , that I have acquired this reputation on account of nothing else than a sort of wisdom. What kind of wisdom is this? Just that which is perhaps human wisdom. For perhaps I really am wise in this wisdom; and these men, perhaps, 20e of whom I was just speaking, might be wise in some wisdom greater than human, or I don’t know what to say; for I do not understand it, and whoever says I do, is lying and speaking to arouse prejudice against me. And, men of Athens , do not interrupt me with noise, even if I seem to you to be boasting; for the word which I speak is not mine, but the speaker to whom I shall refer it is a person of weight. For of my wisdom—if it is wisdom at all—and of its nature, I will offer you the god of Delphi as a witness.