He. Dear, I must be gone 
  While night Shuts the eyes 
  Of the household spies; 
  That song announces dawn. 
 
She. No, night's bird and love's 
  Bids all true lovers rest, 
  While his loud song reproves 
  The murderous stealth of day. 
 
He. Daylight already flies 
  From mountain crest to crest 
 
She. That light is from the moon. 
 
He. That bird... 
 
She.                     Let him sing on, 
  I offer to love's play 
  My dark declivities.
William Butler Yeats
http://www.poemhunter.com/poem/parting-3/