In Nathaniel Hawthorne's "Young Goodman Brown," what happened before the beginning of the story? How do you know about it?

At some point prior to the beginning of the story, young Goodman Brown had met his companion, who we later find out to be the Devil, before. Brown says to him, "'having kept covenant by meeting thee here, it is my purpose now to return whence I came.'" In other words, he says that he's kept to their agreement by meeting this man in the forest tonight, but now—having kept that contract—he plans to return home right away. They would have had to be together before now in order to make the arrangements to meet at this time and place.

Further, the Devil says that, long before Goodman Brown was even born—and therefore before the beginning of the story—he'd been "'well acquainted'" with Brown's family. He knew his grandfather and father, and helped them both to hurt others: one, to "'[lash] a Quaker woman,'" the other, to burn an Indian village with "'a pitch-pine knot kindled at [the Devil's] own hearth.'" He claims that Brown's father and grandfather were both good friends of his.