業精於勤 [业－于－]

Jyutping jip6 zing1 jyu1 kan4
Pinyin yè jīng yú qín

Definitions (CC-CEDICT)
  1. mastery of study lies in diligence (idiom). You can only master a subject by assiduous study.
  2. Excellence in work is only possible with diligence.
  3. Practice makes perfect.