An unshakable belief in something without need for proof or evidence(noun)
WordNet. Princeton University. 2010.
Use "strong belief" in a sentence
"In summary, it is my strong belief that, by keeping the faith, thé"
"Mr. Bunce was in the employment of certain copying law-stationers in Carey Street, and had a strong belief in the law as a profession; — but he had none whatever in the House of Commons."
"The legend of the Noctambule, or the little black man, who appeared to Ninon when she was at the age of twenty years, and promised her perpetual beauty and the conquest of all hearts, was revived, and there was enough probability in it to justify a strong belief in the story."