The Pali Canon, Majjhima Nikaya 26, the Ariyapariyesana Sutta

This is the Ariyapariyesana Sutta, the Discourse on the Noble Search, from the Majjhima Nikaya of the Pali Canon, one of the earliest surviving textual accounts attributed to the Buddha's own description of his search and awakening. As a primary canonical text preserved and transmitted within the Theravada Buddhist textual tradition since antiquity, it carries the strongest possible authority for what that tradition holds the Buddha to have said about his own path, though like any orally transmitted ancient text it reached its written form generations after the events it describes. Its limit is the ordinary one for any ancient scripture, a text of faith and transmitted memory rather than an independently verifiable historical record, so a claim resting on its precise historical accuracy as opposed to its doctrinal content needs to be stated as what the tradition holds rather than as settled biography.