1
general::
A superstition, as in Toads cause warts? That's an old wives' tale. This expression was already known in ancient Greece, and a version in English was recorded in 1387. Despite invoking bigoted stereotypes of women and old people, it survives.
American Heritage Idioms
2
general::
Phrase(s): an old wives’ tale
Fig. a myth or superstition. • You really don’t believe that stuff about starving a cold do you? It’s just an old wives’ tale.
McGrawhill's American Idioms And Phrasal Verbs