冤冤相報 [－－－报]

Jyutping jyun1 jyun1 soeng1 bou3
Pinyin yuān yuān xiāng bào

Definitions (CC-CANTO)
  1. one might suffer from terrible consequences when all they had in mind is revenge/revenge has been taken by both opposing parties on each other endlessly
Definitions (Wiktionary)
  1. phrase, idiomatic
    vengeance begets vengeance