Don’t have my speakers connected so can’t here what is said, but........
Carson backs claim of Trump
http://www.nbcnews.com/video/carson-backs-trumps-claim-of-people-cheering-on-9-11-572643907814
Ben Carson walks back comment about Muslims cheering 9/11
http://www.cbsnews.com/news/carson-claims-he-saw-muslims-cheering-on-911-during-news-coverage/
So which is it?...........
If you're looking for someone to back up what Trump, or anyone else says, then I wouldn't consider Carson the gold standard of facts.