religion vs religious belief

religion and religious belief both are nouns.

Word	Noun	Adjective	Verb	Adverb
religion	Yes	No	No	No
religious belief	Yes	No	No	No

As nouns, religion and religious belief are synonyms defined as:

religion and religious belief: a strong belief in a supernatural power or powers that control human destiny

Other synonyms of religion include faith.

religion (noun)	religious belief (noun)
a strong belief in a supernatural power or powers that control human destiny	a strong belief in a supernatural power or powers that control human destiny
an institution to express belief in a divine power