One version is that his father entrusted him with the money and that he debased it, in consequence of which the father was imprisoned and died, while the son fled, came to Delphi, and inquired, not whether he should falsify the coinage, but what he should do to gain the greatest reputation; and that then it was that he received the oracle.
On reaching Athens he fell in with Antisthenes. Being repulsed by him, because he never welcomed pupils, by sheer persistence Diogenes wore him out. Once when he stretched out his staff against him, the pupil offered his head with the words, “Strike, for you will find no wood hard enough to keep me away from you, so long as I think you've something to say.” From that time forward he was his pupil, and, exile as he was, set out upon a simple life.
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.