It's a lie started thirty years after Darwin's death by a creationist looking to advance a political agenda. It continues to be spread by creationists, partly through ignorance.
It has no basis at all, and has been rejected by Darwin's children, historians and even by creationist groups.
Let's be honest. It's an outright lie, and anyone who spreads it has either been hoodwinked by liars or is a liar himself. I'm presuming that he is the former, but now he knows better.
The Widow Denny "testified inconsistantly"
"It's a lie started thirty years after Darwin's death by a creationist looking to advance a political agenda."
From what I've read he (Darwin) recanted it just before he died.