I'll let the English majors duke it out over what's proper or not - we're just here to investigate its origins.
|"Hund im Schnee liegend" by Marc Franz (1910-1911). Public Domain.|
The phrase - an idiom meaning to let an issue rest rather than to stir up trouble by bringing it up - can be traced back to the late 14th century. Oral tradition probably predates its mention by famous author Chaucer in 1374, but his use of the concept in reverse form is the earliest known example in print.
In the poem, Pandarus advises Crisedye, 'It is nought good a slepyng hound to wake.' (Dude had that one right. Same with cats!)
Jump forward 200 years, and British author and poet John Heywood (1497-1580) advises that 'It is ill wakyng of a sleapyng dogge.'
Finally, around Charles Dickens' time, the phrase is ordered the way we use it today: "Let sleeping dogs lie -- who wants to rouse them?" (David Copperfield, 1850).
Three out of three kitties agree: not us!
TROILUS AND CRISEYDE by Geoffrey Chaucer, line 764
The Proverbs ad Epigrams of John Heywood , 1592, page 132
David Copperfield by Charles Dickens, 1850, chapter 39
Heavens to Betsy! by Charles Earle Funk (Harper & Row, New York, 1955)