Appeal to God (6)
(Other definitions for prayer that I've seen before include "An appeal to a deity" , "Paternoster, for example" , "Appeal (to God)" , "Addressed God" , "Small chance" .)
'appeal to god' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for pray that I've seen before include "Appeal to higher authority" , "Beseech" , "follow religious practice" , "May I ask" , "Invoke" .)