养痈成患（養癰成患）　

◎ 养痈成患 yǎngyōng-chénghuàn

(1) [a carbuncle neglected becomes the bane of your life—leaving evil unchecked spells ruin] 比喻姑息宽容坏人坏事,结果受到祸害

真是养痈成患,将来他的羽翼越多,越难动手哩。——清· 李汝珍《镜花缘》

(2) 也说“养痈遗患”