Initially, prose saying further unnecessary bits (7)
I believe the answer is:
padding
'initially prose saying further unnecessary bits' is the definition.
I can't judge whether this defines the answer.
'initially prose saying' is the wordplay.
I cannot really understand how this works, but
'saying' could be 'adding' (adding is a kind of saying) and 'adding' is present in the answer.
A single letter 'p' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for padding that I've seen is " Soft stuffing".)