The most common and most likely answer to this crossword clue is the 5 letter word LAUDS
I've seen this crossword clue in Financial Times
L
A
U
D
S
Buddy explains!
The straight part
We know that "Prayer service" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case prayer service = lauds.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LAUDS mean?
LAUDS noun- Praise or glorification.
- Hymn of praise.
- (in the plural, also Lauds) A prayer service following matins.
- To praise, to glorify