I was sure the phrase was from a Shakespearean sonnet. The phrase is not, but the sentiment is in Sonnet 16:
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 wandering barque,
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 proved,
I never writ, nor no man ever loved.
Oils on canvas, designed as a basic repeat [Fabric: currently set @ 337 ppi, proofed @ 150 ppi; Wallpaper: 150 ppi; Decal: 210 ppi; Gift wrap: 363 ppi]. © Su Schaefer 2013