Now That's Funny!

Mel Brooks and Carl Reiner originally performed the '2000 Year Old Man' routine only for parties. People kept telling them to put it out as a record, but they demurred. Until, at one party, George Burns came up to them, took his cigar out of his mouth, smiled and said "If you don't, I will."

I thought I got that from Mark Evanier's page (at: http://www.povonline.com/ ) but now I can't find it. If someone can tell me where it's from I'll attribute it properly.