Eventually, they decided it would be best to let sleeping dogs lie and not discuss the matter any further.
1868 August 29, “Sleeping Dogs”, in The Saturday Review of Politics, Literature, Science, and Art, volume 26, number 670, page 287:
But, leaving novelists alone, on the whole we find in real life that if speech is silvern, silence is essentially golden, and that more harm is done by saying too much than by saying too little; above all, that infinite mischief arises by not letting sleeping dogs lie.
2016, Helene Becker, Let Sleeping Dogs Lie, Orca Book Publishers, →ISBN, page 217:
Sometimes you just had to let stuff go. Endlessly rehashing old hurts just made things worse. It was far better, I'd learned, to let sleeping dogs lie.
Japanese: 寝た子を起こすな(ねたこをおこすな, neta ko o okosu na), 触らぬ神に祟りなし(さわらぬかみにたたりなし, sawaranu kami ni tatari nashi, literally “if you don't touch a deity, it will not curse you”)