When working with the Bean Validation API (JSR 303) it can be very practical to have the API sources at hand (e.g. as "Java Source Attachment" in Eclipse).
While the API binary can be retrieved from the JBoss Maven repository, no source JAR is deployed there as of March 2009.
But as the API sources are hosted at JBoss' public subversion repository, you can either read them online or check them out with any SVN client.
Using a SVN command line client the current release of the API 1.0.CR1 can be fetched by
svn co http://anonsvn.jboss.org/repos/hibernate/beanvalidation/tags/v1_0_CR1/