飲馬投錢 [饮马－钱]

Jyutping jam2 maa5 tau4 cin4
Pinyin yìn mǎ tóu qián

Definitions (CC-CANTO)
  1. literally: 'to pay even for a horse's drink of water', to describe the extreme honesty of someone who does not seek private gain at public expense, who has integrity and probity