Chap. XVI. Of Antisthenes and Diogenes. Antisthenes invited many to learn Philosophy of him, but none came. At last, growing angry, he would admit none at all, and therefore bade Diogenes be gone also. Diogenes continuing to come frequently, he chide and threatened him, and at last struck him with his Staff. Diogenes would not go back, but persisting still in desire of hearing him, said, “Strike if you will, here is my head, you cannot find a Staff hard enough to drive me from you, until you have instructed me.” Antisthenes overcome with his perseverance, admitted him, and made him his intimate Friend.
Source: Thomas Stanley, translator (1665) Claudius Aelianus His Various History