Plutarch, Aussprüche von Spartanern (Moralia 219 A):

Archidamos III. war König von Sparta von 361 bis 338 v.u.Z.

When he [sc. Archidamos] invaded Arcadia, he learned that the Eleans were supporting the Arcadians, and so he sent this letter to them: “Archidamus to the Eleans. Quiet is a good thing. [Ἀρχίδαμος Ἠλείοις. καλὸν ἡσυχία (1).]”

[Plutarch: Moralia III. Ed. by Frank Cole Babbitt. Cambridge (Mass.)/London ⁷2004, pp. 310 sq.]

(1) Diogenes Laërtios I 97 schreibt diesen Ausspruch einem der Sieben Weisen zu: Periander.