Almost everything known about Benedict's life as a narrative, as opposed to the Rule he wrote, comes from a single source: Book Two of the Dialogues attributed to Pope Gregory the Great, composed roughly half a century after Benedict's death and built substantially around miracle stories illustrating his sanctity, in keeping with the conventions of the hagiographic genre rather than the standards of a modern biography.
Historians generally treat the broad outline, Benedict's withdrawal to Subiaco, his founding of Monte Cassino, and his authorship of the Rule that shaped Western monastic life for centuries afterward, as reasonably well founded, while treating the specific miracle episodes with the same caution scholars apply to comparable hagiography from the period generally. A minority of scholars have gone further and questioned aspects of the Dialogues' own authorship and transmission, a genuinely debated position within the field rather than a settled consensus, though most historians of the period continue to accept Gregory's authorship while still reading the miracle content as devotional rather than documentary. What is not in serious dispute is the Rule of Saint Benedict's own enormous and well documented influence, since its manuscript spread and adoption across European monasteries is independently traceable, giving Benedict's most important legacy a stronger evidentiary footing than the narrative details of his life as such.