鷸蚌相爭，漁翁得利
鹬蚌相争，渔翁得利
yùbàngxiāngzhēng,yúwēngdélì
- lit. when the snipe and the clam grapple with each other, the fisherman catches them both (idiom)
- fig. when two sides are locked in dispute, it's often a third party that benefits