I first heard this story told by Suzanne Houston at Heads and Tales Story Café in Ringwood three years ago. She had come across it in Doctors on afternoon television, where it provided the framework for a sad story of Afghani refugees. [You can watch it here.] There are various versions on the net, e.g. this one, but when I tell it I’m afraid I emphasise the poor relationship already existing between the farmer and his wife, and I also stress that the neighbour is thinking of deceiving the wife, and saying that the jar of coins was missing or empty, before he opens it and finds the poisonous snake [I only have one – it’s a small jar, and I don’t want any animals harmed in my stories, if I can help it]. This makes it clear that we find what we seek.
Quite recently, I found a reference to another occurrence of the story – not as a main story, but as an aside about women’s inability to keep a secret – presumably the story itself was well-known enough in another contexts for the teller to refer to it briefly but clearly. The source is also Afghan – more particularly Pashtun.
Most recently, I came across a version of it in a tale from Africa, though it seems to be from East Africa, and influenced by Islam, which may account for the transmission, since the story itself has the feel of a Sufi tale.