You need to have the sshd and syslog configured to log the messages. This can be achieved by modifying the /etc/ssh/ssd_config file.
According to sshd manual pages
SyslogFacility -
Gives the facility code that is used when logging messages from sshd(8). The possible values are: DAEMON, USER, AUTH, LOCAL0,LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. The de-fault is AUTH.
What you need to do is modify the syslogfacility parameter in sshd_config file
For egs.
SyslogFacility LOCAL6
Now add the following lines in /etc/syslog.conf
LOCAL6 /var/log/ssh_logs
Restart syslog and sshd