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.
Now for some seventy days they lived in this way all together; then all the rest, except the Athenians and any Siceliots and Italiots that had joined the expedition, were sold.
The total number of prisoners taken, though it is difficult to speak with accuracy, was nevertheless not fewer than seven thousand.