So today we had a practice match, and I landed my ball on the green from 150 out. I repaired my ball mark and then went to mark my ball. When I picked up my ball I noticed it had mud on it so I grabbed my towel and cleaned it off. My partner told me "You know that is a stroke penalty, right?" I disagreed and told him that I can clean off my ball if it was lying on the green, and I marked it. He proceeded to tell me that it would be a penalty, but never enforced it.
I forgot to ask my coach before I left so I just decided to come and ask you guys if I was right. A second question also, if a ball has mud on it but is not on the green, can I clean off my ball as long as I marked where it last was? And if I can do I need to ask my playing partners first?