Where are the database username and password stored? I'd like to send my Drupal installation to a colleague, but I don't want him to see the username and the password of my database. Where are these informations stored?

I've seen that the username and the password are written in sitename/sites/default/settings.php, but is it the only file with these informations? Is it sufficient if I change the username and the password in this file and then send my colleague all my Drupal files and my database?
The settings are stored in sites/default/settings.php. That is indeed the only file with that information and it is sufficient that you change the username and the password in that file.