He called him backwards but there is no proof this was specifically an insult to Khabib's religion.
To be fair Khabib is from a backwards country - they are decades behind the west in terms of equality, infrastructure, attutides etc. Khabib himself has some backwards attitudes with regards to music, young people enjoying themselves etc. He tried to get a hip hop concert shut down for no reason.
It seems to me that Conor specifically avoided insulting Khabib's religion. It's low-hanging fruit and the fact that nobody can provide any actual quotes is surely proof that Conor made an effort not to go there.