The History of the Grecian War (1.56.2-1.57.2)

For whilst the Corinthians studied to be revenged, the Athenians, who had their hatred in jealousy, commanded the citizens of Potidaea, a city seated in the Isthmus of Pallene, a colony of the Corinthians but confederate and tributary to the Athenians, to pull down that part of the wall of their city that stood towards Pallene, and to give them hostages, and also to send away and no more receive the Epidemiurgi (magistrates so called) which were sent unto them year by year from Corinth, fearing lest through the persuasion of Perdiccas and of the Corinthians they should revolt and draw to revolt with them their other confederates in Thrace.

These things against the Potidaeans, the Athenians had precontrived presently after the naval battle fought at Corcyra.

For the Corinthians and they were now manifestly at difference; and Perdiccas, who before had been their confederate and friend, now warred upon them.