Mishna Berura Siman 11 Day 1

The Threads Have To Be Woven. How do you make strings? You take woolen thread and you weave them. Some have a custom even to comb the wool. That's what he brought down in the other Mishnah. Some have the minhag (custom) even to cut off the wool from the sheep. They said, “That’s already; you don’t have to.” But there’s a law. We’re going to see why you have to do lishmah (for its sake), l'shem tzitzit (for the sake of tzitzit). Rama says the minhag is to be lenient when it comes to combing. But the teviya (spinning) is to be lenient when it comes to combing. Yeah, you have to do it.