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 wrong, taking them by surprise. The Lacedaemonians replied that they should not have gone on and announced the truce at Lacedaemon if they were of the opinion that the Lacedaemonians were already wronging them, but they had done this as though they did not think so, and they themselves had not kept on bearing arms against them anywhere
after the announcement of the truce. But the Eleans persisted in the same statement, saying that they could never be persuaded that the Lacedaemonians were not guilty; if, however, they were willing to restore Lepreum to them, they would give up their own half of the fine, and what was due to the gods they would themselves pay on their behalf.
When the Lacedaemonians refused this offer, the Eleans proposed that they should not restore Lepreum, if they objected to that, but, as they eagerly desired to have access to the sanctuary, that they should go up to the altar of Olympian Zeus and swear in the presence of the Hellenes that they would assuredly pay the fine later.