In the newest episode (S7E4), Bran is being given the Valyrian steel dagger from Littlefinger. Bran is mostly silent this whole time. But he says something to Peter that I couldn't make out, and Peter seems to be stunned (as everyone seems to be nowadays) upon hearing the line in question. I even looked at it again, but what did Bran say and what was its meaning?
Chaos is a ladder
The reason Littlefinger is so stunned is because he says the same to Varys when they had a private meeting in the Throne room in an earlier season. This was Bran's way of showing Littlefinger that he knew he was lying when he said he didn't know who the dagger belonged to.
Here's the clip of when Bran says it to Littlefinger:
This is when Littlefinger says it to Varys: