Saw (saying)

A saw is an old saying or commonly repeated phrase or idea; a conventional wisdom. While "old saw" is a common phrase for "saw", some consider it a tautology.

Among various synonyms for "saying", dictionaries from 18th century singled out "saw" as a vulgar, uneducated wisdom, often based in supersititions. This flavor is seen in the expressions "old women's saws" and "old wife's saws."

...
Wikipedia