Prefer knowledge to wealth, for the one is transitory, and the other perpetual.

Actually from Isocrates, it can be found on p. 213 of Classical Rhetoric in English, 1650-1800: A Critical Anthology, part of a 1703 translation of a letter Isocrates wrote to his friend Demonicus which begins on p. 210. Earliest source found attributing it to Socrates was an 1875 book called The Best Reading.