The Little Mermaid

from 'Den Lille Havfrue', Hans Christian Andersen (1836):

...“We have given our hair to the witch,” said (her sisters), “to obtain help for you, that you may not die to-night. She has given us a knife: here it is, see it is very sharp. Before the sun rises you must plunge it into the heart of the prince; when the warm blood falls upon your feet they will grow together again, and form into a fish’s tail, and you will be once more a mermaid, and return to us to live out your three hundred years before you die and change into the salt sea foam.

"Haste, then; he or you must die before sunrise. ... Kill the prince and come back; hasten: do you not see the first red streaks in the sky? In a few minutes the sun will rise, and you must die.”

And then they sighed deeply and mournfully, and sank down beneath the waves..."