How to get query to return rows where first three characters of one row match another row?

Here's my data:

with first_three as 
    (
    select 'AAAA' as code  from dual union all
    select 'BBBA' as code  from dual union all
    select 'BBBB' as code  from dual union all
    select 'BBBC' as code  from dual union all
    select 'CCCC' as code  from dual union all
    select 'CCCD' as code  from dual union all
    select 'FFFF' as code  from dual union all
    select 'GFFF' as code  from dual )
    select substr(code,1,3) as r1 
    from first_three
    group by  substr(code,1,3)
    having count(*) >1 

This query returns the characters that meet the cirteria. Now, how do I select from this to get desired results? Or, is there another way?

Desired Results

BBBA
BBBB
BBBC
CCCC
CCCD

Copyright Notice：Content Author:「zundarz」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/21009318/how-to-get-query-to-return-rows-where-first-three-characters-of-one-row-match-an