Did you try to run a query Florin posted? If you can't access DBA_SOURCE, you need to acquire privileges to do so. Or, if a package is located in a schema you have access to, you could use USER_SOURCE instead.
Because, it runs perfectly well.
Code:
SQL> SELECT Text
2 FROM USER_SOURCE
3 WHERE TYPE = 'PACKAGE BODY'
4 AND NAME = 'PKG_DEGIS'
5 ORDER BY LINE;
TEXT
----------------------------------------------
package body pkg_degis as
function f_dg_admin (par_user in char)
return boolean
is
<snip>