“…so listen carefully.”
So far I’ve discovered it on a cup and on a sign, but the Internet has only offered one source, and that one source is Dorothy Parker.
It does kinda sound like something she might have said. But so do lots of things she didn’t actually say.
So, source and cite, please. If it was DP I ought to be able to find it somewhere, I’ve got her collected works.
The old TV show Hee Haw had a segment called The Gossip Girls that was introduced by a song with the lyrics:
*“Now, we’re not ones to go ‘round spreadin’ rumors,
Why, really we’re just not the gossipy kind,
No, you’ll never hear one of us repeating gossip,
So you’d better be sure and listen close the first time!” *
Okay, thanks. (Somehow I thought it was older than that.)
It probably IS much older than that… but that’s where I heard it first.
It sounds like something Mae West would have said,which would tie in to the Heehaw reference since she was an extremely well known star in her day while Ms Parker was not really Heehaw material ;). But I haven’t found a source. 
I really wasn’t saying that I believed the song from Hee Haw was the origin. I just remembered it from my childhood and pointed out it states the same idea with a slightly different phrase. I would imagine the phrase has been around long before *Hee Haw *.
“If you can’t say anything nice, come sit next to me” is attributed to Alice Roosevelt Longworth.
I searched on google books and found a whole bunch of references in the 1966 to 1969 time frame. They usually reference a matron at a bridge party, though the exact wording varies. I’m guessing that it was a common joke that was going around at the time.
Here’s the oldest:
“My dears,” gushed the matron at the bridge party, “my resolution this year is never to repeat gossip, so for heaven’s sake listen carefully the first time.”
Hee Haw started in 1969 so the phrase definitely existed before them.
I agree that the phrase is probably older than that, but there’s a 1966 cite for you.
I get that. I was pointing out that one doesn’t expect that Dorothy Parker and/or The New Yorker are quoted on Heehaw. Which is an argument against her as the source.