Plato Alcibiades 2 150d (Loeb)

   Socrates:  Do you not remember saying that you were in great perplexity, lest perchance you should ask for evil, [150c] supposing that you were asking for good?

   Alcibiades: I do.

   Socrates: You see, then, how unsafe it is for you to approach the God with your prayers, for it may chance that when he hears your irreverent speech he will reject your sacrifice altogether, and make you partake of other evils as well.
   In my opinion, therefore, it is best to keep silence: for I expect you will not consent to use the Spartan's prayer, you have such a 'highmindedness' -- to give it the fairest of folly's names. 
   [150d] It is necessary, therefore, to wait until we can learn how we should behave towards the Gods and towards men.

   Alcibiades: Well, how long must I wait, Socrates, and who is to be my teacher? For I feel I should very much like to see who the man is.

   Socrates: It is he who takes an especial interest in you. But I think, as Homer relates how Athena removed the mist from the eyes of Diomede,

 
That he might well discern both God and man,

   Alcibiades: Let my instructor remove the mist or whatever else he likes to call it: for I am prepared to obey every one of his commands, without shirking, whoever the man may be, so long as I am to be the better for them.