Plutarch, Aussprüche von Spartanern (Moralia 218 A):

Ariston war König von Sparta 560 bis 510 v.u.Z.

When someone commended the maxim of Cleomenes, who, on being asked what a good king ought to do, said, “To do good to his friends and evil to his enemies [τοὺς μὲν φίλους εὐεργετεῖν τοὺς δὲ ἐχθροὺς κακῶς ποιεῖν],” Ariston said, “How much better, my good sir, to do good to our friends, and to make friends of our enemies? [καὶ πόσῳ κρεῖττον, ἔφη, ὦ λῷστε, τοὺς μὲν φίλους εὐεργετεῖν τοὺς δὲ ἐχθροὺς φίλους ποιεῖν;]” This, which is universally conceded to be one of Socrates’ maxims (1), is also referred to Ariston.

[Plutarch: Moralia III. Ed. by Frank Cole Babbitt. Cambridge (Mass.)/London ⁷2004, pp. 302-305]

(1) Nicht dem Wortlaut, aber dem Sinne nach vgl. Platon: 1. Kriton 49a-e, 2. Gorgias 469a-c, 3. Der Staat 335b-e.