Ascribed source of many rhymes before long (4)
I believe the answer is:
anon
I believe this clue is a double definition.
'ascribed source of many rhymes' is the first definition.
(as in anonymous poems by 'anon')
'before long' is the second definition.
(synonyms)
(Other definitions for anon that I've seen before include "Presently - unattributed" , "Mystery writer" , "Having no known name" , "In the near future" , "Not identified by name" .)