养虎伤身（養虎傷身）　

◎ 养虎伤身 yǎnghǔ-shāngshēn

[bringing up a tiger one sustains injury himself——to be injured by one whom one has been kind to] 饲养老虎,伤及自身。比喻纵容坏人,害了自己

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》