People who will pass on fashionable blaspheming? (6,3)
I believe the answer is:
mortal sin
'blaspheming?' is the definition.
The answer and definition are not the same part of speech.
'people who will pass on fashionable' is the wordplay.
I cannot really see how this works, but
'people' could be 'mortals' ('mortal' can be a synonym of 'person') and 'mortals' is found in the answer.
'fashionable' could be 'in' (in can mean fashionable or trendy) and 'in' is found within the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for mortal sin that I've seen before include "It causes the death of the soul - not venial" , "heinous act" .)