只要功夫深，铁杵磨成针
zhǐ yào gōng fu shēn , tiě chǔ mó chéng zhēn
cf idiom 磨杵成針|磨杵成针, to grind an iron bar down to a fine needle (idiom); fig. to persevere in a difficult task
If you work at it hard enough, you can grind an iron bar into a needle.; to study diligently