Saying from the Bible on making a mistake (8)
I believe the answer is:
averring
'saying' is the definition.
('aver' can be a synonym of 'say')
'the bible on making a mistake' is the wordplay.
'the bible' becomes 'av'.
'on' means one lot of letters go next to another.
'making a mistake' becomes 'erring' ('err' can be a synonym of 'make a mistake').
'av'+'erring'='AVERRING'
'from' acts as a link.
(Other definitions for averring that I've seen before include "Stating firmly and positively" , "Making assertion" .)