人无横财不富，马无夜草不肥
rén​wú​hèng​cái​bù​fù, mǎ​wú​yè​cǎo​bù​féi

windfall wealth

人无横财不富，马无夜草不肥 (人無橫財不富，馬無夜草不肥) rén​wú​hèng​cái​bù​fù, mǎ​wú​yè​cǎo​bù​féi
windfall wealth
a person cannot become wealthy without windfall profits (or ill-gotten gains), just as a horse cannot get fat without night feed

Sources
Definitions
CC-CEDICT