Is this what you're alluding to? In chapter 5 of Mark Twain, Business Man,
S. C. Webster quotes his mother, Annie Moffett Webster:
"When I think of Uncle Sam during those early years it is always
as a singer. He would sit at the piano and play and sing by the hour, the
same song over and over:--
There was an old horse
And his name was Jerusalem.
He went to Jerusalem,
He came from Jerusalem.
Ain't I glad I'm out of the wilderness! Oh! Bang!
. . . .
"Another of Uncle Sam's songs which seems to have struck me as a
classic to be remembered was:--
Samuel Clemens! the gray dawn is breaking,
The howl of the housemaid is heard in the hall;
The cow from the back gate her exit is making,--
What, Samuel Clemens? Slumbering still?
Remember how seldom a buckwheat you get,
How long it may be e'er you see one again,
It may be for years, and it may be forever!
Then why thus tempt fortune, most reckless of men?"
Oh, well, I guess you had to be there!
I have seen other references to the "Jerusalem" song, though I can't put my
finger on any of them just at the moment. Ron Powers says that in some
accounts the horse is named "Methusalem."