Unquestionable truth (6)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
'unquestionable truth' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for gospel that I've seen before include "sacred text" , "The teachings of Christ in a Book of the New Testament" , "The teaching of Christ" , "Christian doctrine" , "Evangel" .)