William Shakespeare - Sonnet CLIII

Cupid laid by his brand, and fell asleep:
A maid of Dian's this advantage found,
And his love-kindling fire did quickly steep
In a cold valley-fountain of that ground;
Which borrow'd from this holy fire of Love
A dateless lively heat, still to endure,
And grew a seething bath, which yet men prove
Against strange maladies a sovereign cure.
But at my mistress' eye Love's brand new-fired,
The boy for trial needs would touch my breast;
I, sick withal, the help of bath desired,
And thither hied, a sad distemper'd guest,
But found no cure: the bath for my help lies
Where Cupid got new fire--my mistress' eyes.

William Shakespeare

http://www.poemhunter.com/poem/sonnet-cliii/