Passage of prose in Steinbeck shows genius (8)
I believe the answer is:
einstein
'genius' is the definition.
(as in Albert Einstein)
'passage of prose in steinbeck' is the wordplay.
'passage of' indicates a hidden word (a passage or extract from the clue).
'EINSTEIN' is hidden within 'prose in steinbeck'.
'shows' is the link.
(Other definitions for einstein that I've seen before include "Mathematical genius of nineties" , "German physicist of relativity" , "Brilliant physicist" , "Bright chap" , "Scientist - seen in it (anag)" .)