Mahabharata 3.67.18

3.67.18

yathā ca vo na jānīyāccarato bhīmaśāsanāt |
punarāgamanaṃ caiva tathā kāryamatandritaiḥ || 18 ||

I have heard it from thee that kindness is the highest virtue. Speaking so, if anybody answereth you, that person should by all means, be known, and ye should learn who he is, and where he dwelleth. And ye foremost of regenerate ones, do ye bring me the words of him who hearing this your speech will chance to answer. Ye should also act with such care that no one may know the words ye utter to be at my command, nor that ye will come back to me. And ye should also learn whether that answers is wealthy, or poor, or destitute of power, in fact all about him.'