FMF Fatty pipe.  Best guess is it was on a 1998 to 2001 cr 125 because that is what bikes we had back then.  Pipe has push in dent in the back as shown on the pictures.  It will need to be polished back up but is in good shape.   Not 100% on the fitment, we also worked on several different bikes for friends at our house.  Thanks for looking.