There is no source of which I am aware.

I first encountered this story when I was a small boy attending a Lutheran summer camp. We did it as a skit. The members of the cabin group would line up by height. The tallest would run "on stage" (e.g. at a campfire) and shout "The Viper is coming in ten minutes." This would continue, in descending order of height and with progressively shorter periods within which the Viper was expected to appear. Finally, at the end, the shortest kid in the cabin would come "on stage" carrying a bucket and a squeegie and announce, in his best mock Dutch accent, "I am der viper; Aye come to vipe der vinders." It was then obligatory to laugh, as if one hadn't seen the skit the year before (and the year before that). Come to think of it, it may have been written by Martin Luther.