One Piece Chapter 52, page 7: OATH

Sanji and the other Baratie cooks gasp in shock as they notice Luffy's body stretching. "WHAT'S THAT!?" Sanji exclaims. Luffy launches himself forward, stretching his arms far behind him as he flies toward Mihawk, roaring "ARGHHHHHH!". On the wreckage of his flagship, Don Krieg watches in surprise, muttering, "THAT BRAT...! HE MUST BE A DEVIL FRUIT USER!".