In the Arthurian legend "Gawain and the Green Knight", The Green Knight appears at Arthur's court and calls all his knights young boys.
And to prove his boast he says the following:
"And if any in this house holds himself so hardy and is so boldblooded and so utterly mad that he dare strike one stroke for another in return, I will give to him this costly axe, that is heavy enough, and he shall handle it if he likes, and I will bide the first blow as bare as I sit here. If any fellow here be so brave as to do what I say, let him come forward quickly and take hold of the weapon, and I will quit claim upon it for ever. It shall be his very own. And I will stand strongly on this floor to abide his stroke if thou wilt doom him to receive another stroke in return from me; yet will I grant him delay.
I'll give to him the blow,
In a twelvemonth and a day.
Now think and let me know
Dare any herein aught say"
So Gawain rises to the challenge and knocks the Green Knights head clean off. But the fellow doesn't fall, he picks up his head and informs Gawain that he expects to see him in a year "to receive such a blow as thou hast given."
Read the rest of the poem here if you want to know how it went:
http://rpo.library.utoronto.ca/poem/62.html