I was checking this, but not find the proper one. So I prepared one and sharing that query here.
SELECT
n.nspname,
b.usename,
p.proname,
p.prosrc
FROM
pg_catalog.pg_namespace n
JOIN pg_catalog.pg_proc p ON
pronamespace = n.oid
join pg_user b on
b.usesysid = p.proowner
where
nspname not in ('information_schema',
'pg_catalog')
This was really helpful. There is a very small mistake, missed out the schema name for pg_user.
SELECT
n.nspname,
b.usename,
p.proname,
p.prosrc
FROM
pg_catalog.pg_namespace n
JOIN pg_catalog.pg_proc p ON
pronamespace = n.oid
join pg_catalog.pg_user b on
b.usesysid = p.proowner
where
nspname not in ('information_schema',
'pg_catalog')