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.

And it was his son, Sitalces, whom the Athenians wanted to make their ally, wishing him to help in subduing the places on the coast of Thrace and Perdiccas.

So Nymphodorus came to Athens, brought about the alliance with Sitalces, and got Sadocus son of Sitalces made an Athenian citizen; and he promised also to bring the war in Thrace to an end, saying that he would persuade Sitalces to send the Athenians a Thracian force of cavalry and targeteers.