Every evil in the bud is easily crushed: as it grows older, it becomes stronger.

[Omne malum nascens facile opprimitur; inveteratum fit pleurumque robustius.]

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

Philippics [Philippicae; Antonian Orations], No. 5, ch. 11 / sec. 31 (5.11/5.31) (43-01-01 BC) [ed. Hoyt (1896)]
    (Source)

(Source (Latin)). Other translations:

Every evil is easily crushed at its birth; when it has become of long standing, it usually gets stronger.
[tr. Yonge (1903)]

Every evil at its birth is easily suppressed; but if it be of long standing, it will offer a stouter resistance.
[ed. Harbottle (1906)]

Every evil is easily crushed at its birth; become inveterate it as a rule gathers strength.
[tr. Ker (Loeb) (1926)]

Every evil is easily nipped in the bud; with age it usually gets stronger.
[tr. Manuwald (2007)]