old wives' tale

noun

1. a traditional belief, story, or idea that is often of a superstitious nature.

noun

1. a belief, usually superstitious or erroneous, passed on by word of mouth as a piece of traditional wisdom

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.