And I think it may be this - Hillary Clinton's interview with Katie Couric on November 26, 2007. You can watch it at that link.
It's the one where this exchange occured:
"If it's not you, how disappointed will you be?" Couric asked.Wow. Wouldn't it be nice if that was it?
“Well, it will be me,” she said.
But she said she would stand behind any other Democratic nominee, if it came to that. “We're going to have unified party, behind whoever we nominate.”
Clearly, she has considered the possibility she won't be the nominee?
"No, I haven't," Clinton said.