The World's Best Jokes, Christian Clippings, p. 26
A stranger entered the church in the middle of the sermon and seated himself in the back pew. After a while he began to fidget. Leaning over to a white-haired man at his side, evidently an old member of the congregation, he whispered:
"How long has he been preaching?"
"Thirty or forty years, I think," the old man answered.
"I'll stay then," decided the stranger, "He must be nearly done."