In the middle of a storm, the three witches have gathered together.
Thunder and lightning. Enter three Witches
When shall we three meet again
In thunder, lightning, or in rain?
When the hurlyburly's done,
When the battle's lost and won.
That will be ere the set of sun.
Where the place?
Upon the heath.
There to meet with Macbeth.
I come, Graymalkin!
Fair is foul, and foul is fair:
Hover through the fog and filthy air
Shakespeare, William, Macbeth, Act 1, Scene 1.