History of the Peloponnesian War

Sitalces then was commanding at once Chalcidice, Bottica, and Macedonia, and was ravaging them all. But when none of the objects for which he made the expedition was being gained by him, and he found his army without provisions and suffering from the severity of the weather, he was persuaded by Seuthes the son of Spardacus, who was his nephew and next in authority to himself, to return with all speed. For Seuthes had been secretly won over by Perdiccas, who promised to give him his sister, and a sum of money with her.

Thus persuaded then, after remaining [in the enemy's country] thirty days in all, and eight of them in Chalcidice, he retired home with his army as quickly as he could: and Perdiccas subsequently gave his sister Stratonice to Seuthes, as he had promised. Such were the events that happened in the expedition of Sitalces.