The Memorabilia by Xenophon
I remember listening to another argument of his, the effect of which would be to promote self-examination. The listener must needs be brought to ask himself, "Of what worth am I to my friends?" It happened thus. One of those who were with him was neglectful, as he noted, of a friend who was at the pinch of poverty (Antisthenes). Accordingly, in the presence of the negligent person and of several others, he proceeded to question the sufferer.
Socrates. What say you, Antisthenes?--have friends their values like domestic slaves? One of these latter may be worth perhaps two minae, another only half a mina, a third five, and a fourth as much as ten; while they do say that Nicias, the son of Niceratus, paid a whole talent for a superintendent of his silver mines. And so I propound the question to myself as follows: "Have friends, like slaves, their market values?"
Not a doubt of it (replied Antisthenes). At any rate, I know that I would rather have such a one as my friend than be paid two minae, and there is such another whose worth I would not estimate at half a mina, and a third with whom I would not part for ten, and then again a fourth whose friendship would be cheap if it cost me all the wealth and pains in the world to purchase it.
Well then (continued Socrates), if that be so, would it not be well if every one were to examine himself: "What after all may I chance to be worth to my friends?" Should he not try to become as dear as possible, so that his friends will not care to give him up? How often do I hear the complaint: "My friend So-and-so has given me up"; or "Such an one, whom I looked upon as a friend, has sacrificed me for a mina." And every time I hear these remarks, the question arises in my mind: If the vendor of a worthless slave is ready to part with him to a purchaser for what he will fetch--is there not at least a strong temptation to part with a base friend when you have a chance of making something on the exchange? Good slaves, as far as I can see, are not so knocked down to the hammer; no, nor good friends so lightly parted with.
 Antisthenes, "cynicorum et stoicorum parens." Cic. "de Or." iii. 17; "ad Att." xii. 38. See below, III. iii. 17; "Symp." passim; Diog. Laert. II. v.; VI. i.
 A mina = L4 circ.
 For Nicias see Thuc. vii. 77 foll.; "Revenues," iv. 14; Plut. "Nic." IV. v.; Lys. "de bon. Aristoph." 648.