I just answered your other post.
Have you cut the 5" squares yet? Or is the fabric still in yardage?
If you haven't cut the fabric yet, you do have the option of prewashing. Some people do and some people don't. I personally don't prewash. If I suspect a fabric might bleed, I test a small piece with water and a white cloth to see if any dye transfers out of the fabric. Not prewashing keeps the sizing in the fabric, which helps stabilize the fabric throughout the piecing and quilting process. People who prewash their fabric often iron with starch before cutting, to restore stability to the fabric.