rsync -azP -e 'ssh -i /path/to/id_rsa_private_key' /files/source destination_host_user@111.111.111.111:/destination/path
Be sure to add ssh-add /path/to/id_rsa_private_key
-a
It stands for "archive" and syncs recursively and preserves symbolic links, special and device files, modification times, group, owner, and permissions.