Someone who demands physical evidence in order to be convinced (especially when this demand is out of place) WordNet 3.0 & Open English WordNet

A doubting Thomas is a skeptic who refuses to believe without direct personal experience – a reference to the Gospel of John's depiction of the Apostle Thomas, who, in John's account, refused to believe the resurrected Jesus had appeared to the ten other apostles until he could see and feel Jesus's crucifixion wounds. Wikipedia

Skeptic who refuses to believe without direct personal experience. Wikipedia Disambiguation

Episode from Gospel of John, in which the Apostle Thomas refused to believe that the resurrected Jesus had appeared to the ten other apostles Wikidata