Condemn piece of prose (8)
I believe the answer is:
sentence
I believe this clue is a double definition.
'condemn' is the first definition.
('sentence' can be a synonym of 'condemn')
'piece of prose' is the second definition.
(Other definitions for sentence that I've seen before include "Court judgement" , "Judge's punishment" , "See 11" , "Grammatical unit and prison term" , "unit booked?" .)