First off, credit where credit is due. Islamicfinder.org is who is actually providing the date.

The plugin and instructions to use the plugin are located in its github page:

http://github.com/abdulvayani/islamic_date

If you would like this plugin to work with your mephisto blog or site, here is a different version of this plugin.

http://github.com/abdulvayani/mephisto_islamic_date

NOTE: Installation of the gem Hpricot by Why the Lucky Stiff is needed.

Working example of this plugin can be found here.