That man must be everyone’s personal enemy who has behaved like a public enemy to his own friends. No wise man ever felt that a traitor ought to be trusted.

[Omnium est communis inimicus qui fuit hostis suorum. Nemo umquam sapiens proditori credendum putavit.]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

In Verrem [Against Verres; Verrine Orations], Action 2, Book 1, ch. 15 / sec. 38 (1.15.38) (70 BC) [tr. Greenwood (1928)]
    (Source)

(Source (Latin)). Alternate translations:

He is the common enemy of all men who has once been the enemy of his own connections. No wise man ever thought that a traitor was to be trusted
[tr. Yonge (1903)]

He is a common enemy who has been a foe to his own people. No man of sense has ever considreed a traitor worthy of credence.
[ed. Harbottle (1906)]