What poem does "a world in a sand and a heaven in a flower" come from?

"A world in a grain of sand and a heaven in a flower" comes from the naive prediction of the English poet Blake.

The specific full text is as follows:

See a world in a grain of sand.

There is a heaven in a wild flower.

Hold infinity in the palm of your hand.

Eternity will melt in an hour.

See the world in a grain of sand.

See heaven in a flower.

Hold infinity in the palm of your hand.

A moment is eternity.

Appreciation: In the classical language theory of traditional Buddhism, there is a famous saying: "A flower is the world and a leaf is bodhi". A flower can see the whole world, and a leaf can represent the whole bodhi tree. Buddhism is a profound knowledge, and many profound philosophies are beyond the reach of our growing young minds. Similarly, I can only make some shallow guesses about this famous saying that often haunts my ears.