The Beam is a German fairy tale

Fairy tale

A fairy tale is a type of short story that typically features such folkloric characters, such as fairies, goblins, elves, trolls, dwarves, giants or gnomes, and usually magic or enchantments. However, only a small number of the stories refer to fairies...

 collected by the Brothers Grimm

Brothers Grimm

The Brothers Grimm , Jacob Grimm and Wilhelm Grimm , were German academics, linguists, cultural researchers, and authors who collected folklore and published several collections of it as Grimm's Fairy Tales, which became very popular...

as tale 149.It is Aarne-Thompson type 987, False Magician Exposed by Clever Girl, with an episode like type 1290, A Fool Mistakes a Flax Field for a Lake.

Synposis

A magician shows a rooster carrying a beam. A girl carrying a four-leafed clover realizes and declares that it is just a straw, not a beam. When she marries, the magician enchants her to think she sees a stream, and then breaks it after she has hiked up her skirts to cross.