懲前毖後 [惩－－后]

Jyutping cing4 cin4 bei3 hau6
Pinyin chéng qián bì hòu

Definitions (CC-CEDICT)
  1. lit. to punish those before to prevent those after (idiom); to criticize former mistakes firmly to prevent them happening again
Definitions (Wiktionary)
  1. phrase, idiomatic
    to criticize former mistakes firmly to prevent them happening again