‘Qurbani’ of ‘khsahi’(castrated)(male goat with fertility destroyed) is legal and Sunnat

Speech of  opposition :They say that it is not legal to sacrifice Qurbani of khashi.

What is said in Islam :Qurbani of khashi is Sunnate Huzur Pak Sallallahu Alaihi Wasallam. Which is written in many Hadish Shareef. So how can that be inlegal although Huzur Pak Sallallahu Alaihi Wasallam did that?  Saying that inlegal is kufri.