Plutarch, Solon
Bernadotte Perrin, Ed.

Now it so happened that Aesop, the writer of fables, was in Sardis, having been summoned thither by Croesus, and receiving much honor at his hands. He was distressed that Solon met with no kindly treatment, and said to him by way of advice: ‘0 Solon, our converse with kings should be either as rare, or as pleasing as is possible.’ ‘No, indeed.’ said Solon, ‘but either as rare or as beneficial as is possible.’ [2]

At this time, then, Croesus held Solon in a contempt like this; but afterwards he encountered Cyrus, was defeated in battle, lost his city, was taken alive and condemned to be burnt; and then, as he lay bound upon the pyre in the sight of all the Persians and of Cyrus himself, with all the reach and power of which his voice was capable, he called out thrice:(1) ‘O Solon!’ Cyrus, then, astonished at this, sent men to ask him what man or god this Solon was on whom alone he called in his extremity. [3] And Croesus, without any concealment, said: ‘This man was one of the sages of Greece, and I sent for him, not with any desire to hear or learn the things of which I stood in need, but in order that he might behold, and, when he left me, bear testimony to the happiness I then enjoyed, the loss of which I now see to be a greater evil than its possession was a good. For when it was mine, the good I derived from it was matter of report and men's opinion, but its departure from me issues in terrible sufferings and irreparable calamities which are real. [4] And that man, conjecturing this future from what he then saw, bade me look to the end of my life, and let not insecure conjectures embolden me to be proud and insolent.’ When this was reported to Cyrus, since he was a wiser man than Croesus, and saw the word of Solon confirmed in the example before him, he not only released Croesus, but actually held him in honor as long as he lived. And thus Solon had the reputation of saving one king and instructing another by means of a single saying.