A South American once enthralled by Egyptian god in religious epic (8)
I believe the answer is:
ramayana
'religious epic' is the definition.
(Sanskrit epic)
'a south american once enthralled by egyptian god' is the wordplay.
'south american once' becomes 'Mayan' (one of the Maya people).
'enthralled by' indicates putting letters inside ('enthral' can mean 'capture').
'egyptian god' becomes 'Ra' (Ra is an example).
'a'+'mayan'='amayan'
'amayan' put into 'ra' is 'RAMAYANA'.
'in' acts as a link.
(Other definitions for ramayana that I've seen before include "Sanskrit epic" , "Indian epic poem" , "1 28 [EPIC POEM]" .)