琴瑟和鳴 [－－－鸣]

Jyutping kam4 sat1 wo4 ming4
Pinyin qín sè hé míng

Definitions (CC-CEDICT)
  1. in perfect harmony
  2. in sync
  3. lit. qin and se sing in harmony
Definitions (粵典–words.hk)
  1. 語句
    以琴​同瑟​兩種​樂器​能夠​協調​合奏​，​比喻​夫妻​和​合
    (of married couples) to get along harmoniously; literally: harmony of Guqin and Chinese Zither, two musical instruments
Definitions (Wiktionary)
  1. phrase, idiomatic, of a married couple
    in perfect harmony