How do I use Freenode IRC with SASL in Adium?
Adium 1.5 doesn't support using SASL for IRC. That will be added in 1.6: https://trac.adium.im/ticket/14478.

In 1.6, there will be a checkbox to activate SASL. When that is activated, the password field is treated as the SASL password.

The following build can be used successfully: Adium_1.6hgr5915.dmg

And this guide may help if you have question using it after you've enabled SASL.