History of the Peloponnesian War

But Astyochus did not even think of punishing Alcibiades, especially as he no longer came within his reach as formerly, but going up to Magnesia to visit him and Tissaphernes he not only told them the contents of the letter he had received from Samos, himself becoming an informer, but also attached himself, as it was said, to Tissaphernes for his own private gain, both in this and in other matters; and it was for this reason that in dealing with the question of the pay, which was not being paid in full, his insistence was rather feeble.

Alcibiades immediately wrote a letter against Phrynichus to the authorities at Samos, telling them what he had done and urging that he be put to death.

Phrynichus was exceedingly disturbed, since he was in the very greatest danger on account of the information he had given; he accordingly wrote again to Astyochus, reproaching him because his former information had not been concealed, as in honour it should have been, and adding that now he was ready to furnish the Lacedaemonians the opportunity to destroy the whole Athenian army at Samos, stating in detail how he could do this, since Samos was without walls; it was not culpable in himself, he concluded, now that he was in danger of his life through their actions, to do this or anything else rather than perish himself at the hands of his bitterest enemies. But Astyochus gave information of this also to Alcibiades.