to include source files in the jar, this would suffice:
<jar destfile="${my.lib}/${myProject}.jar" basedir="${eclipse.workspace}/${myProject}" includes="bin/**,src/**"/>
however, you've mwntioned create an executable jar
in your question, for that, this should work:
<target name="abc">
...
<manifest file = "MANIFEST.MF">
<attribute name = "Main-Class" value = "yourClassName"/>
<attribute name = "Class-Path" value = "."/>
</manifest>
<jar destfile="${my.lib}/${myProject}.jar" basedir="${eclipse.workspace}/${myProject}" includes="bin/**,src/**" manifest="MANIFEST.MF"/>
</target>