Madara states that Hashirama's the only one
who can stop him, but that won't be happening because Hashirama's "no longer with us."
I don't want any bull**** about that being in past tense because of "could" or whatever (either way, could doesn't always refer to the past); if Madara was talking about the past he wouldn't have any need to mention the fact that Hashirama's "no longer with us."
A couple months later, as Naruto's failing to defeat Madara, Orochimaru revives Hashirama,
thus bringing back the only person who could/can beat him
(as said by Madara, Dan, and, indirectly, the author):
It you still refuse to believe it, I don't know how Kishi can make it any more obvious. I guess you'll just have to wait until Hashirama and Madara have a reunion on the battlefield.