History of the Peloponnesian War
Thucydides
Thucydides, Vol. 1-4. Smith, Charles Foster, translator. London and Cambridge, MA: Heinemann and Harvard University Press, 1919-1923.
The Lacedaemonians said that they had done what was possible; for they had restored the prisoners of the Athenians that were in their hands, had brought back their troops in Thrace, and had done whatever else had been in their power. As to Amphipolis, however, they said that they were not in control of it, so as to deliver it up;
but they would try to bring the Boeotians and Corinthians into the treaty and to get back Panactum, and would recover all Athenian prisoners that were in the hands of the Boeotians. Pylos, however, they insisted the Athenians should restore to them;
or at any rate, they should withdraw the Messenians and the Helots, as they themselves had withdrawn their troops from Thrace, and the Athenians themselves might garrison the place if they wished. After many and frequent conferences had been held during this summer, they persuaded the Athenians to withdraw from Pylos the Messenians, the rest of the Helots, and all who had deserted from Laconia;