How to Know When Oracle User Password Changed?

Oracle database internal table SYS.USER$ contains useful information about users and roles. Some of the columns have got following meaning:

• NAME – name for user or role
• TYPE# – 0 for role or 1 for user
• CTIME – the date of creation
• PTIME – the date the password was last changed
• EXPTIME – the date the password has last expired
• LTIME – the date the resource was last locked
• LCOUNT – number of failed logon

SQL> SELECT
        name,
       ctime,
       ptime
FROM
      sys.user$
WHERE
      name = 'SYS';

NAME                 CTIME     PTIME
-------------------- --------- ---------
SYS                  31-MAR-16 11-MAY-21