The exact wording commonly used today appeared in the 19th century in The London Magazine. This old phrase originated in the 13th century. Later in the 14th century, it was used by Geoffrey Chaucer in one of his books that says it's good to avoid waking a sleeping dog. The expression “let sleeping dogs lie” was a popular proverb from the 13th century, alluding to waking up a fierce guard dog and causing problems.
Beyond the mention of the dog, this seems to be a more general, albeit not disconnected, plea to avoid getting involved in the problem of others. Republican presidential hopeful Donald Trump, who never let sleeping dogs lie, got up clearly early Friday morning (Sputnik News). You can use the phrase “let sleeping dogs lie down” when you're trying to tell a person not to disturb the current situation or environment. Most commonly used to state that something should be allowed to rest, usually a discussion or debate, the phrase “let sleeping dogs lie” has a history that dates back to the 13th century.
The saying “let the sleeping dogs rest” was one of the favorites of Sir Robert Walpole, the first prime minister of Great Britain, who exerted considerable influence over King George I and King George II from 1721 to 1742. There are several references in the etymological discussions of the phrase, for example, to a text called Proverbia Vulgalia et Latina that translates as “Common and Latin Proverbs”, but the text is almost impossible to find. If you let sleeping dogs lie, you're avoiding the conflagration of a potentially volatile situation. Although taken from a poem of around 100 words by Chaucer, it should be noted that this is not evidence that he invented such idioms, simply that Chaucer expected that phrase to be understood by his audience. For example, if you're wondering if you should wake your baby, it might be a good idea to let dogs sleep to prevent them from crying when they wake up.
The meaning of the expression “let sleeping dogs lie” is to avoid any disturbance in a scenario that could cause a conflagration that leads to problems or frustration. The one who passes and meddles in conflicts that do not belong to him, is like one who takes a dog by the ears. The phrase is a request that a matter or incident not be discussed or avoided, where addressing it could cause problems. But how can we not use the pun “let sleeping dogs lie” on last week's EP when Tony and Camila drunkenly fought and ended up getting kicked off the show? (The Observer).
While the government seems to let sleeping dogs lie, there is concern that a re-elected NDP gang will end the hybrid model and only support publicly owned continuous care centers with 100% unionized staff.