I tried above example but it was not showing more than 4000 characters then I modified it little bit and was able to get whole stored procedure definition. Please see the updated script below -
SELECT SCHEMA_NAME(O.SCHEMA_ID) [SCHEMA_NAME], O.NAME, OBJECT_DEFINITION(OBJECT_ID) TEXT
FROM SYSCOMMENTS AS C
INNER JOIN SYS.OBJECTS AS O ON C.ID = O.[OBJECT_ID]
INNER JOIN SYS.SCHEMAS AS S ON O.SCHEMA_ID = S.SCHEMA_ID
WHERE OBJECT_DEFINITION(OBJECT_ID) LIKE '%FOO%'
ORDER BY SCHEMA_NAME(O.SCHEMA_ID), O.NAME