Infallible

a. [Prefix in, not, and fallible; It. infallibile, Sp. infalible, Fr. infaillible.]

1. Not fallible; not capable of erring; entirely exempt from liability to mistake; unerring; inerrable. “Of opinion that their infallible master has a right over kings.” Dryden.
2. Not liable to fail, or to deceive confidence; sure not to disappoint or fail; certain; as, infallible evidence; infallible success.

To whom also he showed himself alive, after his passion, by many infallible proofs. Acts i. 3.