This subject has been exhausted. There are those of us and many authors of books who only recommend prewashing fabric before quilting. I remember when cotton fabric used to shrink, and we looked for labels (for clothing) that said preshrunk which meant it would only shrink 2 to 3 percent. Muslin on the other hand will shrink more than once so it should be washed on hot and dried twice. To those of you who do not prewash, if you havent had a problem, it is just a matter of time. I saw a beautiful quilt posted here about a year ago where the woman had worked countless hours piecing (think it was hand done) and then one of the stronger blues ran onto the light(white) fabric. I spend too much time to have a problem that could have been avoided by just 1 extra step.
Pat