Mass book (6)
I believe the answer is:
missal
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">mass book</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for missal that I've seen before include "Book of church texts" , "Prayer-book" , "Book of prayers and rites" , "Religious book" , "book needed to get through service" .)