Trump gave a speech to law enforcement in Long Island, New York. He remarked,

“When you see these towns and when you see these thugs being thrown into the back of a paddy wagon, you just see them thrown in, rough, and I said, ‘Please don’t be too nice.'”

USA Today – Trump tells law enforcement: ‘Don’t be too nice’ with suspects
ABC News – Trump to police: ‘Please don’t be too nice’ to suspects