养虎伤身yǎng hǔ shāng shēn

饲养老虎，伤及自身。比喻纵容坏人，害了自己。

例兀术听了，大叫道：“罢了，罢了！此乃养虎伤身也！”——清·钱彩《说岳全传》

英bringing up a tiger one sustains injury himself——to be injured by one whom one has been kind to;