The history to which you refer was enacted by the South Park kids as follows: (the "dumb, dumb, dumb, dumb" were sung like they were accompanying drum beats)
Gary Sr.: Well, you remember Martin Harris, the rich man who wrote down what Joseph Smith read out of the hat?
Stan: Yeah.
Gary Sr.: See, after he was done, he took some of the pages of what would become the Book of Mormon home. [Back to the 1800s, night, the large building]
Singers: Martin went home to his wife Dumb dumb dumb dumb dumb And showed her pages from the Book of Mormon Dumb dumb dumb dumb dumb
Harris: A-and so Joseph Smith put his head into a hat, a-and read to me what the golden plates said. I wrote it all down and we're gonna publish it into a book.
Mrs. Harris: Martin, how do you know he isn't just making stuff up and pretending he's translating off golden plates?
Singers: Lucy Harris smart smart smart Smart smart smart smart smart
Harris: Why would he make it up?
Singers: Martin Harris dumb dadumb-
Lucy: All right, here. I'm gonna hide these pages. [puts them in a drawer at the bottom end of an armoir] If Joseph Smith really is translating off of golden plates, then he'll be able to do it again. But if Joseph Smith is making it all up, then the new translations will be different from these.
Harris: Okay, fine. I bet he'll have no problem. [puts on his coat and heads out]
Singers: Lucy Harris smart smart smartMartin Harris dumb. So Martin went on back to Smith Said the pages had gone away Smith got mad and told Martin He needed to go pray Dumb dumb dumb dumb dumb
Harris: [upon Smith's return] Look, ah I'm sorry about losin' the pages we worked on, Joe, but I'm ready to write it all down again if you translate from the plates.
Smith: I would love to, Martin, except, I just had a vision. And the Lord said he's very angry with me for letting you take those pages.
Harris: [gasps] He is??
Singers: Dumb dumb dumb dumb dumb
Smith: Yes. He is so mad that he will never let me translate from the plate of Lehi again. He's... we must now translate from the plate of Nephi. So it will be the same basic story, but written a little differently.
Harris: Wow! If God got angry with you, then you must be tellin' the truth.
Singers: Dumb dumb dumb dumb dumb dumb dumb.
Harris: All right, Martin. Let's get to work! [Smith reads from the hat again and dictates to Harris, who writes it all down] [Back to the present, the Marsh house]
Gary Sr.: And that's how it happened.
Kids: Yeah! All right! [the Marshes sit there without a word to say] Stan: ...Wait. Mormons actually know this story and they still believe Joseph Smith was a prophet?
Brilliant episode but I found this to be the most telling part
>>Gary: Listen, I just wanted to let you know you don’t have to worry about me tryin’ to be your friend anymore.
Stan: I don’t?
Gary: Look, maybe us Mormons do believe in crazy stories that make absolutely no sense, and maybe Joseph Smith did make it all up, but I have a great life. and a great family, and I have the Book of Mormon to thank for that. The truth is, I don’t care if Joseph Smith made it all up, because what the church teaches now is loving your family, being nice and helping people. And even though people in this town might think that’s stupid, I still choose to believe in it. All I ever did was try to be your friend, Stan, but you’re so high and mighty you couldn’t look past my religion and just be my friend back. You’ve got a lot of growing up to do, buddy. Suck my balls. [turns around and walks off. All four boys just look at him in wonder, even Cartman.]
Cartman: Damn, that kid is cool, huh? <<