Tsunade says: "Did my grandfather really fight against this
Notice how Tsunade is looking up as she makes her statement. Also notice how Tsunade says "this". That would imply that Tsunade was referring to an inanimate object (PS) when making her statement.
I pointed the aforementioned out so I could cut down any confusion on who/what Tsunade was referring to when making her statement.
Madara responds to Tsunade with: "I already told you that the only one who can stop me is Hashirama."
Now...why does Madara say this?...because he is answering the question that Tsunade had just asked. He indirectly answers her question by saying only Hashirama can defeat me. In other words, Madara doesn't literally say the words "Hashirama can beat my PS", but this is understood since:
1. Madara says Hashirama is "the only one who can stop me"
2. There's no way Madara could have defeated Hashi without using his full power since Madara needed the kyuubi's help to fight Hashi (Hashi must have just been that strong)
Madara throws out another hint that Hashi has fought PS when he says: "Plus, I should say that it's probably a good thing for you that he is not here...Because..."
Madara then proceeds to use PS power to destroy some mountains as seen below:
Then Madara says this:
Madara: "If I'm the only one here...The extent to which the maps will need to be drawn won't be too drastic."
Madara saying the above statement implies that Madara and Hashi have had battles to where they have devastated the battlefield. Which of Madara's powers/techs can devastate a battlefield? PS can which he had just demonstrated when he destroyed those mountains.
This is a great and definitive indication that Madara has used PS against Hashirama.