防患于未然
fáng​huàn​yú​wèi​rán

to nip in the bud

  1. 防患 fáng​huàn
    to take preventative measures
    to prevent disaster, accidents, or trouble from occurring; to guard against potential harm
  2. 于 於 yú preposition
    in
    Indicates a location, scope, or time; equivalent to 在 zài
  3. 未然 wèi​rán
    before it happens
    (literary) describes a situation that has not yet happened or become a reality; often used in the context of preventing trouble before it starts