A parable by Barlaam the Hermit, in the Caxton’s translation of the Legenda Aurea.
An archer took a little bird called a nightingale, and when he would have slain this nightingale there was a voice given to the nightingale which said: O thou man, what should it avail thee if thou slay me? Thou mayst not fill thy belly with me, but and if thou wilt let me go, I shall teach thee three wisdoms, that if thou keep them diligently thou mayst have great profit thereby. Then he was abashed of his words and promised that he would let him go if he would tell him his wisdoms. Then the bird said: Study never to take that thing that thou mayst not take. And of things lost which may not be recovered, sorrow never therefor. Ne believe never thing that is incredible. Keep well these three things, and thou shalt do well. And then he let the bird go as he had promised. And then the nightingale flying in the air said to him: Alas! thou wretched man, thou hast had evil counsel, for thou hast lost this day great treasure. For I have in my bowels a precious margaret which is greater than the egg of an ostrich. And when he heard that, he was much wroth and sorrowed sore because he had let her go, and enforced him all that he could to take her again, saying: Come again to my house and I shall show to thee all humanity, and give to thee all that shall need thee, and after shall let thee go honourably whereas thou wilt. Then said the nightingale to him: Now I know well that thou art a fool, for thou hast no profit in the wisdoms that I have said to thee. For thou art right sorrowful for me whom thou hast lost which am irrecuperable, and yet thou weenest to take me where thou mayst not come so high as I am; and furthermore where thou believest to be in me a precious stone more big than the egg of an ostrich, when all my body may of not attain to the greatness of such an egg. And in like wise be they fools that adore and trust in idols, for they worship that which they have made, and call them whom they have made keepers of them.