路遥知马力，日久见人心

路遙知馬力，日久見人心
lùyáozhīmǎlì,rìjiǔjiànrénxīn
just as distance determines the stamina of a horse, so does time reveal a person's true heart (proverb)

CEDICT

Entry Composition

1 路遥知马力 lùyáozhīmǎlì a long road tests a horse's strength; distance tests a horse's stamina; only time can reveal a person's true strength
2 日久见人心 rìjiǔjiànrénxīn time reveals a person's heart; time will tell a true friend from a false one