Islams revised service book (6)

I believe the answer is:

missal

'service book' is the definition.
(thesaurus)

'islams revised' is the wordplay.
'revised' is an anagram indicator.
'islams' is an anagram of 'MISSAL'.

(Other definitions for missal that I've seen before include "Book of church texts" , "Mass medium" , "Catholic mass text book" , "service manual" , "Book used at Catholic mass" .)

I've seen this clue in The Irish Independent.

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