惩前毖后懲前毖後

chéng qián bì hòu

ㄔㄥˊ ㄑㄧㄢˊ ㄅㄧˋ ㄏㄡˋ

Idiom

1lit. to punish those before to prevent those after (idiom); to criticize former mistakes firmly to prevent them happening again