In the chapter 882 of One Piece ("Beyond the Expectations of a Yonkou")
This assumes that he has knowledge of both Luffy's Gear 4th technique and the mecanism to activate it. However, Luffy never mentionned it in his fight against him, so it is the first time he sees both Luffy and his technique.
How so ? Is it something that is known over Devil Fruit users, and everyone who ate them has "gears" like Luffy ?