Yeah, the literal document by Ken Schwaber and Jeff Sutherland that says what Scrum is.
https://www.scrum.org/resources/scrum-guide
Some quotes to keep in mind:
> As Scrum is being used, patterns, processes, and insights that fit the Scrum framework as described in this document, may be found, applied and devised. Their description is beyond the purpose of the Scrum Guide because they are context sensitive and differ widely between Scrum uses. Such tactics for using within the Scrum framework vary widely and are described elsewhere.
> Scrum exists only in its entirety and functions well as a container for other techniques, methodologies, and practices.
Burndown charts can be used in Scrum, but are not Scrum. Backlog refinement is an ongoing activity in Scrum, but its precise form is left undefined. Story points can be used in Scrum, but are not Scrum. The Scrum Master is a role which is explicitly defined in the Scrum Guide, but there is nothing there claiming they are there to "drive" anything, only be "true leaders who serve the Scrum Team and the larger organization." The retrospective is defined in the Scrum Guide, but its precise form is left undefined.