Again, when Charmides offered him some slaves in order that he might derive an income from them, he declined the offer; and according to some he scorned the beauty of Alcibiades. He would extol leisure as the best of possessions, according to Xenophon in the Symposium. There is, he said, only one good, that is, knowledge, and only one evil, that is, ignorance; wealth and good birth bring their possessor no dignity, but on the contrary evil. At all events, when some one told him that Antisthenes' mother was a Thracian, he replied, “Nay, did you expect a man so noble to have been born of two Athenian parents?” He made Crito ransom Phaedo who, having been taken prisoner in the war, was kept in degrading slavery, and so won him for philosophy.
Source: Lives of the Eminent Philosophers (1925) by Diogenes Laërtius, translated by Robert Drew Hicks. A Loeb Classical Library edition; volume 1 published 1925; volume 2 published 1925. WikiSource.