Hi,
Refer link : http://www.cisco.com/c/en/us/support/docs/security/asa-firepower-services/118644-configure-firepower-00.html
On ASA :
ciscoasa(config)# policy-map global_policy
ciscoasa(config-pmap)# class sfr
ciscoasa(config-pmap-c)# sfr fail-open monitor-only.
You can set the traffic to monitor only so that it forwards the copy of packet and does not take any action on the packets.
Regards,
Aastha Bhardwaj
Rate if that helps!!!