That's a lie. He never said that. 

This is what he said back in July:

"In looking back at our investigations into mishandling or removal of classified information, we cannot find a case that would support bringing criminal charges on these facts. All the cases prosecuted involved some combination of: clearly intentional and willful mishandling of classified information; or vast quantities of materials exposed in such a way as to support an inference of intentional misconduct; or indications of disloyalty to the United States; or efforts to obstruct justice. We do not see those things here."

https://www.fbi.gov/news/pressrel/press-releases/statement-by-fbi-director-james-b-comey-on-the-investigation-of-secretary-hillary-clinton2019s-use-of-a-personal-e-mail-system