History of the Peloponnesian War

And when Admetus came not long after, he declared who he was, and begged him not to avenge himself on a banished man, for whatever he himself might have urged against any request of his to the Athenians;

for in that case he would receive evil from the king, when he was far his inferior in power; whereas it was the part of a noble nature to avenge itself on its equals [alone], and on fair terms. Besides, he had himself opposed the king with regard to some request merely, and not on a point of bodily safety; whereas he, if he gave him up, (he mentioned by whom and for what he was being pursued, would deprive him of security of life.

And when the Athenians and Lacedaemonians came no long time after, he did not give him up; but as he wished to go to the king, sent him by land to the other sea, to Pydna, which was in Alexander's dominions. There he found a merchant vessel putting to sea for Ionia, and having gone on board, was carried by a storm to the armament of the Athenians, that was blockading Naxos.

In his fear he told the master who he was, (for he was unknown to those in the vessel,) and on what account he was flying; and said, that if he did not save him, he would declare that he was taking him for a pecuniary consideration; that their only hope of safety lay in no one's leaving the vessel till the voyage could be continued; and that if he complied with his request, he would remember him with becoming gratitude. The master did so; and after lying out at sea off the naval encampment a day and a night, subsequently arrived at Ephesus.

And Themistocles rewarded him by a present of money (for there came to him afterwards money from Athens, sent by his friends, and from Argos that which had been secretly laid up there): and having gone up the country with one of the Persians on the coast, he sent a letter to king Artaxerxes, the son of Xerxes, who was lately come to the throne. The purport of the letter was this:

I Themistocles am come to thee, who have done most harm of all the Greeks to your house, as long as I was compelled to defend myself against thy father who had attacked me, but still far more good, when he was retreating in circumstances of safety to me, but of peril to him. And return for a benefit is owed me;

and now I am come with power to do thee great good, being persecuted by the Greeks because of my friendship for thee. But I wish to wait a year, and then explain in person to thee the objects of my coming.