坐山觀虎鬥 [－－观－斗]

Jyutping co5 saan1 gun1 fu2 dau3
Pinyin zuò shān guān hǔ dòu

Definitions (CC-CEDICT)

lit. sit on the mountain and watch the tigers fight (idiom)
fig. watch in safety whilst others fight then reap the rewards when both sides are exhausted

Definitions (Wiktionary)

phrase, figuratively, idiomatic
to watch in safety while others fight, then reaping the spoils when both sides suffer.