Let sleeping dogs lie

As with dogs, sleeping seals are best left in peace.

The phrase "let sleeping dogs lie" has a long history; back in 1374, Geoffrey Chaucer used a similar phrase in his story, Troilus and Criseyde - "It is nought good a sleepyng hound to wake".

Even earlier, the Bible had this to say: "He that passes by, and meddles with strife belonging not to him, is like one that takes a dog by the ears".