proverb/ki vɔ.l‿œ̃.n‿œf vɔ.l‿œ̃ bœf/
once a thief, always a thief (someone dishonest enough to steal a small thing can steal a big thing as well)
Literally, “(he) who steals an egg, steals a cow”. Compare English in for a penny, in for a pound, English one may as well hang for a sheep as a lamb.