佛遺教經論疏節要 1.158

1.158

煩惱毒害己自名蛇，更舉黑蚖喻之可畏。惑在心睡起必害慧，蚖在室睡起必害人。

The poisonous harm of defilement is itself already called a snake, and moreover a black viper is adduced as a metaphor for its frightfulness. When delusions sleep in the mind, when they awaken they will surely harm wisdom; when a viper sleeps in a room, when it awakens it will surely harm people.