By William Shakespeare

Let me not to the marriage of true minds 

Admit impediments. Love is not love 

Which alters when it alteration finds, 

Or bends with the remover to remove. 

O no! it is an ever-fixed mark 

That looks on tempests and is never shaken; 

It is the star to every wand'ring bark, 

Whose worth's unknown, although his height be taken. 

Love's not Time's fool, though rosy lips and cheeks 

Within his bending sickle's compass come; 

Love alters not with his brief hours and weeks, 

But bears it out even to the edge of doom. 

If this be error and upon me prov'd, 

I never writ, nor no man ever lov'd.

This sonnet was first published in 1609. In the 1609 Quarto it is mis-numbered as 119. It is now in the public domain. Wikipedia has a reasonable description of its meaning as well as a short description of why scholars believe it is not, actually, a love poem.