Let sleeping dogs lie

"Let sleeping dogs lie" is an English proverb known at least since the 14th century. This saying suggests that when an old problem is no longer causing anyone trouble, it might be better left undiscussed: "Possibly he cohabited with Miss Bloggs, but don't mention it in front of his wife, let the sleeping dogs lie", and dormant controversies should not be restarted even if they were never resolved. This intent is similar to the meanings of sayings like "Don't rock the boat", "Never trouble trouble till trouble troubles you".

History
An early version in "It is nought good a slepyng hound to wake" belongs to Chaucer (c. 1385 AD, "Troilus and Criseyde", III.764) and is predated by earlier n'ésveillez pas lou chien qui dort, "wake not the sleeping dog" (early 14th century). The Chaucer's character, Pandarus, when uttering the phrase, is speaking literally, referring to Criseyde's ladies sleeping outside her chamber.

The Oxford Dictionary of Proverbs traces the following evolution of the saying:
 * It is euill wakyng of a slepyng dog (1546, John Heywood in "A Dialogue Conteinyng the Nomber in Effect of All the Prouerbes in the Englishe Tongues");
 * It's best To let a sleeping mastiff rest (1681, Samuel Colvil in "The Whigs Supplication");
 * Take my advice and [ask] as little about him as he does about you. Best to let sleeping dogs lie (the first known use of the modern phrasing, 1824, Walter Scott in the "Redgauntlet").

In the 19th century the modern version was already popular. Widespread use in the 20th century (see Bryan and Mieder for some literary sources) made the proverb very recognizable, enabling some significant modifications, from "It is my policy to let sleeping senators lie" (Gore Vidal attacking his opponent Senator S. I. Hayakawa who was prone to napping in the chamber) to “let sleeping dogmas lie” (Edmund Gosse).

Other languages
The Schlafende Hunde ("sleeping dog") was an idiom for a dangerous subject that should not be touched upon since at least the 16th century. The form of expression varies. schlafende Hunde wecken ("to wake the sleeping dogs") is to create an inconvenience to oneself by attracting attention.

non svegliare il can che dorme dates back to c. 1345, when Bosone da Gubbio made a wordplay (non sveglian lo can che dorme) on an gran Can del Catai, the Chinese Emperor.

Expression is known in Russian, usually in the form не буди лихо, пока оно тихо, "don't wake up trouble while it is quiet".

The idiom is unfamiliar to the speakers of Arabic who mostly fail to recognize its meaning.