Barry, I've mislaid the prayer book (8)
I believe the answer is:
breviary
'the prayer book' is the definition.
(breviary is a kind of prayer book)
'barry i've mislaid' is the wordplay.
'mislaid' indicates anagramming the letters.
'barry'+'ive'='barryive'
'barryive' is an anagram of 'BREVIARY'.
(Other definitions for breviary that I've seen before include "service manual" , "Catholic priest's book of daily prayers" , "Church book" , "Book of daily prayer for RC priests" , "Priest's book of prayers found in river bay" .)